Nothing, but I suspect your concept of "religion" is not the same as the parent's. Some people think of religion is a valuable tool humans invented to help them govern their lives . To others, religion is a doctrine that teaches ostensibly facts about the nature of the universe. Typically these facts lead to conclusions such as "humans SHOULD do x, MUST NOT do y", etc.

Two completely different concepts, one word. So it's a bit confusing. But for someone discussing the second type of religion, saying it's "man-made" is definitely a knockout punch.

God was supposed to have created men not the other way around.

It's hypocrisy to claim that religion X is divine revelation only to turn out to be man-made.

I don't think there's anything wrong with religions that acknowledge (and even embrace) the man-made aspect.

Man-made is relatable. It’s understandable. It’s comprehensible. All things that the universe, when considered in its entirety, could never be.