As much as people make Mahomes the face for all that's wrong with how QBs are reffed, Josh Allen actually gets more calls than anybody. That roughing the passer call was almost simultaneous with him touching out of bounds and he was actively throwing.
I don't think Mahomes gets all of the extra special treatment that some like to claim. People are always going to look to come up with something to complain about when rooting against an elite player. There are always going to be more eyes on elite QB's and some will probably get some calls other QB's won't, but I really haven't seen too many egregious calls in his favor.
Josh Allen on the other hand. He is an excellent QB, but he is EASILY the QB that looks for calls the most. I can't stand when he flops, and he makes it beyond obvious. I don't even think it's debatable when it comes to that. For a QB as big and strong as him that runs like he does, his flopping after players and trying to sell the call is embarrassing.
The play you're referring to is just a damn tough play for a defender, especially when it's Josh Allen as he's one of a few QB's that can make that play.