Pay close attention to below slokas from [Bhagavad Gita]:
BG 3.10, 3.11, 3.12, 13
— In the beginning of creation, the Lord of all creatures (Brahma) sent
forth generations of men and demigods, along with sacrifices for
Viṣṇu, and blessed them by saying, “Be thou happy by this yajña
[sacrifice] because its performance will bestow upon you everything
desirable for living happily and achieving liberation.”
— The demigods, being pleased by sacrifices, will also please you, and
thus, by cooperation between men and demigods, prosperity will reign
for all.
— In charge of the various necessities of life, the demigods, being
satisfied by the performance of yajña [sacrifice], will supply all
necessities to you. But he who enjoys such gifts without offering them
to the demigods in return is certainly a thief.
The devotees of the Lord are released from all kinds of sins because
they eat food which is offered first for sacrifice. Others, who prepare
food for personal sense enjoyment, verily eat only sin.
The answer to your question lies within above slokas if you understood those, then no need to read below. If not convinced then before understanding my answer, first consider the below terms.
1. Dharma (not religion)
This answer explains nicely: Dharma is actually a righteous duty. Every element of universe has its own Dharma. Except humans, most of the elements follow their duty but without being conscious about it. If a human follows own Dharma consciously then attains liberation.
e.g. a person might be born Muslim/Vaishnav/Non-believer, but his Dharma depends on his work & nature. For example, if he is in science then BrahminDharma, in army then KshatriyaDharma, in business then VaishyaDharma and doing job (any field) then ShudraDharma.
Similarly, a person has to have SwamiDharma towards his wife, but PitaDharma towards his children and PutraDharma towards parents.
2. Devta (demigods)
If you look at the Indian philosophy, each element of nature is associated with a demigod. e.g. Water => Varun, Air => Vayu, Earth => Bhoomidevi, Light => Suryadev, Humans => Narayan, Animals ==> Pashupati and so on.
When a demigod gets disturbed, it creates a havoc. In other words, Tsunami can be considered as Varun dev is angry. The demigods have to be pleased by maintaining their equilibrium; temples are just gentle reminders.
e.g. People end up worshiping Pashupati in Nepal temple instead of seeing him in animals all over the world.
3. Yajña/Yagna (Sacrifice)
यज्ञ = योग्य त्याग
In modern times, we have mistakenly limited the term Yagna with only Dharmik activity of Hom-Havan. In reality, it is just 1 way of doing it.
If one does his prescribed(योग्य) duty(धर्म) by sacrificing(त्याग) the deviations, then it is Yagna.
e.g. if a student pays attention to study by sacrificing the thoughts of playing then he is doing (Shram) Yagna. Similarly, a boy does Brahmacharya Yagna until he marries his wife.
Refer to various ways of Yagna in
BG 4.25-4.31.
— Some yogīs perfectly worship the demigods by offering different
sacrifices to them, and some offer sacrifices in the fire of the Supreme
Brahman.
— Some [the unadulterated brahmacārīs] sacrifice the hearing process
and the senses in the fire of mental control, and others [the regulated
householders] sacrifice the objects of the senses in the fire of the
senses.
— Others, who are interested in achieving self-realization through
control of the mind and senses, offer the functions of all the senses,
and of the life breath, as oblations into the fire of the controlled
mind.
— Having accepted strict vows, some become enlightened by sacrificing
their possessions, and others by performing severe austerities, by
practicing the yoga of eightfold mysticism, or by studying the Vedas
to advance in transcendental knowledge.
— Still others, who are inclined to the process of breath restraint to
remain in trance, practice by offering the movement of the outgoing
breath into the incoming, and the incoming breath into the outgoing,
and thus at last remain in trance, stopping all breathing. Others,
curtailing the eating process, offer the outgoing breath into itself
as a sacrifice.
— All these performers who know the meaning of sacrifice become
cleansed of sinful reactions, and, having tasted the nectar of the
results of sacrifices, they advance toward the supreme eternal
atmosphere.
— O best of the Kuru dynasty, without sacrifice one can never live
happily on this planet or in this life: what then of the next?
Conclusion
So combine all of above to come to a conclusion. When the Yagna is performed according to own duty(स्वधर्म), then the demigods are pleased and the nature's equilibrium is maintained.
Also refer my answer to below question, where I explain scientifically why non-veg is not preferable in most cases:
Should a Brahmin be Vegetarian.
But have ATTENTION: It doesn't literally mean that killing animals & eating meat is bad and eating veg food is good.
Answer
When someone eats meat or even vegetarian (un)knowingly, is he/she helping maintaining nature's equilibrium? In other words, is he pleasing to Pashupati dev or Bhoomidevi?
It depends.
1 -- A tribal staying in Alaska, African, Andaman have no choice but to depend on killing and eating animal. They please Pashupati, because by killing those animals they keep the number in check and also by protecting the forest resources for harvesting. (Killing too many is wrong though)
2 -- A CEO maintains strictly vegetarian diet and daily gets his favorite veg dish by sending driver 10 km away from his office at lunch time. He might be pleasing Bhoomidevi, but he violates (pollutes) Vaayu devta! Realizing this petrol waste, he then starts eating in office canteen. But wastes food daily due to taste dislike. Now he angers Bhoomi devi!
Coming back to that Muslim boy. If he is eating non-veg food, then definitely he is (un)knowingly committing sin. Because in modern time, availability/nutrition/nature-preserve/varieties of vegetarian food is quite vast, which leaves very less room for non-veg food. Land - Bhoomi devi is wasted for harvesting non-veg.
So everyone's (irrespective of religion) Maanav Dharma is to adopt or try Vegetarianism!
