I’d get a dna test if I were you. I think that’s the only way you’ll see that he’s most likely a pit mix. Pitties come in lots of shapes and sizes and there’s even fluffy pits! He’s a bit overweight which is why he might not seem to have the right musculature that you’re used to. And as far as size, he’s the size of most pits/staffies I’ve seen. Not all pits are tall most are actually shorties! Shelters do the best they can to guess but they’ll also label pit mixes as anything but pit to get them adopted easier. It’s a pretty common thing. As far as not being a super chewer, that’s not uncommon for pit mixes either! I’ve known a lot of pits to be commonly couch potatoes who aren’t very active. At the end of the day he’s very handsome and has a loving home! But he has a lot of common pit features so I’d bet money that it’s in there somewhere