After discussing it after, we learned from another table it was because we were too loud for them.
So instead of asking us to move (as the whole place was empty) or having them move, or even just asking us to keep it down. We were told, "Can you guys like, shut up?" with no reason. And we weren't being loud at all.
That and, it took over an hour total for our drinks and meal to be served, and we were at an IHOP.