Yeah, it really is more like google play store or shopping websites and similiar apps/websites (although there are some that have a better design I guess). I’m not really a fan of it either, but I guess people being used to those (which is probably the majority of the userbase of flatpak) feel more comfortable with it.
My guess with the difference between “trending” and “popular” is that the former means lots of recent downloads and the latter a lot of downloads in a longer timespan (e.g. a year or so)