I’ve lived in different areas of the US including the south. I’ve also heard references to “Jewing down” and similar comments in the south and also from someone in California. It’s a stereotype assumption that these things are only found in the south- they are everywhere ( unfortunately)
Being Jewish in areas where there are mostly Christians, people make the assumption that I am Christian too. Why wouldn’t they assume this?- as most people they meet are. Church in the south is both spiritual and a social community. Being invited to church is an act of hospitality. If someone new moves in the area, they are invited to join the communities there. So at college, another student might ask a new friend to church as a way to make friends.
Once I explain that I am Jewish, most people are respectful of that. It has been rare that someone is not- and even in those cases, it is mostly misinformation, unawareness, or curiosity, not hostility.
However, I think you have to be willing to accept that some things are cultural wherever you live. People have customs. That can include saying “Merry Christmas” to you and, Christmas tree in a public place. I have heard the term “Christian” as an adjective to describe a good. ethical person. So one might hear " He’s a good Christian" but is isn’t an attempt to be exclusive, but a term that has been used for generations. I don’t take any offense at that because I understand the context of how it is being used.
In many communities the churches are the largest buildings and so, other events take place in there, such as meetings and music performances, so it is possible a student may be in a church for one of these events.
If this is something one is uncomfortable with, then some southern colleges are probably not a good fit. However, avoiding the south is not a guarantee that one will avoid hostility or insensitive comments.