Showing a non QH in AQHA shows?

Ok I am pretty dense when it comes to showing. I did 4H when younger then some drill team, barrel racing but no real shows. Now I just do a few playdays and trail ride. I know someone with what looks to be a mostly TB if not TB/QH and they showed in the AQHA regionals. How is that so? I just umed to show AQHA you had to have a QH. Just curiousity. Thanks!