Or their understanding of religion has never extended past Christianity. It’s just the assumption that all religions must operate with the same rules and underlying beliefs of Christianity - like that to practice a religion, you have to believe in God.

Frequently not even "Christianity", which whatever you think of it as a belief system is a vast, diverse, unbelievably complex historical entity. Frequently they've been exposed to Evangelical Christianity, a couple more Protestant denominations, and a few Catholics.

They also tend to behave as vehemently evangelical as some christians do

They never get that Judaism isn’t based on belief! It’s just not a thing!