do yall think he might be mixed with anything??

my family and i got him 2 years ago (embarrassingly and shamefully) from basically a puppy mill (we were super uneducated pls don’t judge 🙏) and were told he was a pure breed boston. but ever since we first got him i couldn’t help but think there’s a mix of something in there or if he was just the special one in his litter (we met his supposed siblings and parents and they all did give off pure bred except him)