Is Kalki avatar a killer of Buddhist?

Question

adhuna kahkula ndsavatdro bauddha pdsanda mlecchadindnca vedadharma setu panpdlandya krtavatarah kalh mpendsman stntva nirayddudhrta vanasi tavdnukampam kimiha kathaydmah

---------Kalki Purana chapter 10 text 30

Meaning:

Recently, You appeared as Lord Kalki in order to eliminate the dynasty of Kali by destroying the Buddhists, atheists, and mlecchas,thereby protecting the true path of religion What more can we say about Your causeless mercy

Answer 1

The answer of your question -Is Kalki Avatara a murderer of Buddhists is No according to Shreemad Bhagvat Purana. Skandha 2 Chapter 7 : SB 2.7 : Scheduled Incarnations with Specific Functions and Skandha 12 chapter 2 : SB 12.2 : The Symptoms of Kali-yuga.

It says -:

यहर्यालयेष्वपि सतां न हरे: कथा: स्यु:
पाखण्डिनो द्विजजना वृषला नृदेवा ।
स्वाध्या स्वधा वषडिति स्म गिरो न यत्र
शास्ता भविष्यति कलेर्भगवान युगांते ॥38॥

yarhy ālayeṣv api satāṁ na hareḥ kathāḥ syuḥ
pāṣaṇḍino dvija-janā vṛṣalā nṛdevāḥ
svāhā svadhā vaṣaḍ iti sma giro na yatra
śāstā bhaviṣyati kaler bhagavān yugānte

Thereafter, at the end of Kali-yuga, when there exist no topics on the subject of God, even at the residences of so-called saints and respectable gentlemen of the three higher castes, and when the power of government is transferred to the hands of ministers elected from the lowborn śūdra class or those less than them, and when nothing is known of the techniques of sacrifice, even by word, at that time the Lord will appear as the supreme chastiser. SB 2.7.38

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विचरन्नाशुना क्षोणयां हयेना प्रतिमद्यूति:।
नृपलिङ्गछ्चदो दस्युन कोटिशो निहनिष्यति॥20॥

vicarann āśunā kṣauṇyāṁ hayenāpratima-dyutiḥ
nṛpa-liṅga-cchado dasyūn koṭiśo nihaniṣyati

Godhead. Displaying His unequaled effulgence and riding with great speed, He will kill by the millions those thieves who have dared dress as kings. SB 12.2.20

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Now if we look at the verse no.38 and verse 20 we can see the exact purpose ok Kalki-Avatara , In Kali-Yuga When there will no Katha-Kirtana will get performed even at the homes of most spiritual oriented people , Brahmana , Kshatriya's and Vaishya's will became atheist (nastika) ,Shudras will became kings ,and there will no sound heard of Swaha ,Swadha and Vashtkara ,at that time Lord will take Kalki avatara to punish Kali-Yuga and those thives who have falsely dressd as kings.

The Kalki will punish Kali-Yuga and demons and nor the buddhist people , it doesn't saying anything about murdering of Buddhists. Buddha is considered a Avatara of Lord Vishnu here.

we can see that the lord himself will assume dress of buddha and will preach false dharma , when Danavas by using knowledge of vedas and becoming invisible reciding in City of Maya Danava ,will cause destruction of the people.

So according to me the answer will be simply No.

Answer 2

Kalki seems to just kill almost every human, with the notable exception of Devapi and Maru. The Mahabharata seems to skirt around this issue, understandably given its controversial nature, but you can tell that's what it really means. It is said in multiple places that the literal definition of a varna is based upon character/behavior, although it is inheritable to a debatable extent. The references to the Chaturvarna there can easily be explained by the other races such as Asuras.

And Markandeya said,

...

And the whole world will be filled with mleccha behaviour and notions and ceremonies, and sacrifices will cease and joy will be nowhere and general rejoicing will disappear. And men will rob the possession of helpless persons of those that are friendless and of wisdoms also. And, possessed of small energy and strength, without knowledge and given to avarice and folly and sinful practices men will accept with joy the gifts made by wicked people with words of contempt.

...

And Brahmanas and Kshatriyas and Vaisyas will disappear, leaving, O king, no remnants of their orders. And all men towards the end of the Yuga will become members of one common order, without distinction of any kind. And sires will not forgive sons, and sons will not forgive sires. And when the end approaches, wives will not wait upon and serve their husbands. And at such a time men will seek those countries where wheat and barley form the staple food.

And, O monarch, both men and women will become perfectly free in their behaviour and will not tolerate one another’s acts. And, O Yudhishthira, the whole world will be mlecchified. And men will cease to gratify the gods by offerings of Sraddhas. And no one will listen to the words of others and no one will be regarded as a preceptor by another.

...

And no one will, at that time, be a giver (of wealth or anything else) in respect to any one else. And the inhabited regions of the earth will be afflicted with dearth and famine, and the highways will be filled with lustful men and women of evil repute. And, at such a time, the women will also entertain an aversion towards their husbands. And without doubt all men will adopt the behaviour of the mlecchas, become omnivorous without distinction, and cruel in all their acts, when the end of the Yuga will come.

...

And he will restore order and peace in this world crowded with creatures and contradictory in its course. And that blazing Brahmana of mighty intellect, having appeared, will destroy all things. And he will be the Destroyer of all, and will inaugurate a new Yuga. And surrounded by the Brahmanas, that Brahmana will exterminate all the mlecchas wherever those low and despicable persons may take refuge."

So Kalki will kill the Buddhists, but it is completely unrelated to them being Buddhists. He just kills every human minus Devapi and Maru (possibly others, but I see no reason to believe so), so kills them for the same reason as all the other humans.

Don't worry though, Kalki leaves the structures intact. Thus, all our hard work will help a new, better race of humans flourish.

And in the age that will set in, viz., the Krita, well-planted gardens and sacrificial compounds and large tanks and educational centres for the cultivation of Brahmanic lore and ponds and temples will re-appear everywhere. And the ceremonies and rites of sacrifices will also begin to be performed. And the Brahmanas will become good and honest, and the regenerate ones, devoted to ascetic austerities, will become Munis and the asylums of ascetics, which had before been filled with wretches will once more be homes of men devoted to truth, and men in general will begin to honour and practise truth.

https://www.wisdomlib.org/hinduism/book/the-mahabharata-mohan/d/doc7469.html#note-e-28433