The Jivatma will remain as a Preta unless Śrāddha is done, but non-Hindus do not perform Śrāddha.
Usana Smriti's Chapter 7 has the following verse:
It is laid down that Sapindikaran, S'raddha should be preceeded by the Daiva, (i.e., offerings made to the Deities). There one should invite the departed Manes and point out again (i.e., invoke) the deceased.* (17)
On this verse the translator/commentator (Manmatha Nath Dutta) says:
A deceased person is called Preta till the celebration of the Sapindikaran Shraddha , after which he is designated Pitri,
So, the answer to your question is a Yes, as per Hinduism (Hindu Scriptures). After death, the Jiva remains as a Preta till all the necessary rites are performed duly.
Sometimes, if persons had unnatural deaths, additional remedies are required to be performed for these souls to be relieved from the Pretahood and attain the Pitrihood.
Many of these remedies are mentioned in Satatapa Smriti's last Chapter:
For one dying of cholera one should treat a century of Brahmanas with sweet edibles. For one killed by fire sticking to the throat one should give away a dhenu of sesame. (48)
For one dying of a disease of the hair one should perform eight Krichchhas. According to this regulation one should perform the funeral rites for them. (49)
Thereupon being freed from the condition of a preta (dead) the gratified Pitris (departed manes) grant sons, grand-sons, longevity, health and wealth. (50) Here ends the [account of the] : fruits [of various] acts given by S'atatapa to his disciple S'arabhanga accosting him with humility, (51)
Therefore, according to Hinduism, anyone dead attains the Preta state. And, to relieve them from this Preta state, some rites are required to be performed, after which the Jivas are elevated to the Pitri state.
(NOTE:- This answer is from the perspective of Hindu scriptures. What happens to the non-followers of Hindu scriptures after their death is something that we shouldn't be concerned about on this site. We can't know that either unless we have knowledge about their rites and scriptures)
In this context, the below sloka from the Bhagavad Gita 2.27 is relevant -
जातस्य हि ध्रुवो मृत्युर्ध्रुवं जन्म मृतस्य च। तस्मादपरिहार्येऽर्थे न त्वं शोचितुमर्हसि।।2.27।।
For those who are born, death is certain. For those who die, (re-)birth is certain. Therefore you should not feel grief for what is inevitable.
(The only exception to the above birth-death cycle is for those who attain moksha, as Krishna himself says elsewhere in the Bhagavad Gita.)
English Translation of Abhinavgupta's Sanskrit Commentary By Dr. S. Sankaranarayan
2.27 Jatasya etc. Destruction comes after birth, and after the destruction comes birth. Thus, this series of birth-and-death is like a circle. Hence to what extent is this to be lamented for ?
Non-Hindus are certainly not an exception to the above rule. After their death, their rebirth is a certainty (assuming they have not attained moksha). There is thus no scope for any jIvAtmA - Hindu or non-Hindu, to remain as preta after death.