This, exactly. I was born and raised in Alabama, where there are no professional sports teams. Everything I've read just now in this thread about Everton v. Liverpool in the city applies to Alabama v. Auburn in the state, but it's a whole state, not just one city. I was born an Alabama fan, as my parents were Alabama fans. My brother is a Bama fan, etc. etc. If you are in Alabama and you meet a stranger, especially during college football season, you're almost certainly getting the "Alabama or Auburn" question (like the "blue or red" mentioned earlier), if you're not already wearing the respective logo all over your clothes. We live with each other every single day of the year (though I live in Georgia now), and the rivalry is always at the forefront of everyone's mind.
So to act like these all-encompassing sports rivalries that permeate all facets of life are unique to the UK football scene does absolutely come across as condescending. I could just as easily say, "you've clearly never been to Alabama."