NRI's are not Hindus because crossing sea and visiting a foreign Land (outside of Bharatavarsha) leads to loss of caste and a Foreigner can't become a Hindu unless he/she degrades himself to a position of a Chandala (Dalit)
1/n

Dharma Sutra of Baudhayana (II.1.2.2) list sea voyages is one of the offense which leads to loss of Caste, this belief was widespread amongst Hindus, because Hindus regarded Non vedic People (foreigners) as Mlechas (impure) and contact with leading to loss of casre 2/n

Such was the widespread Superstition of sea voyages amongst Hindus that Many Mutinies broke out because Britishers wanted Hindus to cross sea to reach Burma. During the First Anglo-Burmese War (1824–26), regiment which consisted mainly of Upper caste Hindus refused to march. 3/n

Portuguese sailors noted that Hindus were reluctant to engage in maritime trade due to the fear of losing caste but some Hindus however Like some Banias didn't prescribe to this rite to gain monetary benefits. 4/n

Preserving Religion and caste were reasons of The 1857 rebellion. Britishers forcing Upper caste Hindus to cross sea was one of the reasons too.General Services Enlistment Act of 1856 required the new recruits to serve overseas if asked. 5/n

These Superstitions just like Untouchability is still present amongst Hindus, a Hindu priest lost his job because he went to London, the voyage leading to loss of his Brahmin caste. 6/n

Now the question is can Foreigners and Non Hindus become Hindus ? Answer is only when they degrade themselves to lowest position in Hinduism called Chandala. Medatithi in Manusmriti 2.23 mentions this while giving definition of Aryavarta and Land pure for Hindus Rituals 7/n

Now NO matter what reasons Liberal Neo Hindus give or tries to act progressive to spread Extinct Black Magic cult of theirs, Traditional and orthdox Hindus still believe in these rules, an American was beaten for entering puri temple even after his conversion to Hinduism 8/n