That's a weird qualification to me, as if most other vegetarians do it because of their religion. I don't have any data/stats, but environmental destruction based on our farming practices, and cruelty to animals, both factor a lot higher than religion (has been my experience anyway, but it might be an interesting difference in the US given the deeply entrenched state of religion there).
If you look up the original Hindu texts, it specifically says you should not eat meat, respect nature and animals; which means you should NOT eat any kind of meat.
Most vegetarians on the Indian subcontinent/Asia in general do not eat meat for religious/cultural reasons. Growing up in a Hindu/Buddhist-adjacent culture is often enough to cause someone to avoid red meat.