I got stuck trying to explain (without being the annoying "well, actually" guy) why my SO's phone wasn't screwed up when switching from ATT to a different carri

I got stuck trying to explain (without being the annoying "well, actually" guy) why my SO's phone wasn't screwed up when switching from ATT to a different carrier. Because on the old SIM it said 5G dammit! Now it only says 4G so how is that not slower??