Revealing mistake: When Stiles enters the locker room, a guy walks out the shower and you can see his black underwear. (00:05:25)
Revealing mistake: After the first game in the locker room, Scott notices a 6 inch long hair on his chest, the hair is visibly taped to his chest with scotch tape.
Revealing mistake: When Stiles opens up his locker there are a pack of cards that have been spread out to give the effect of falling out of the locker as he opens but they are already hanging at first and then they fall with everything else. (00:35:15)
Revealing mistake: You see Scott walking towards the shower and he says hi to Chubby while passing him, but if you look closely after that you can tell Scott's only wearing a mask and his shoulder is bare skin. (01:00:15)
Answer: Because Lewis knew that Scott wasn't being true to himself by letting the Wolf take over his personality. Lewis, like Boof, liked Scott for who he was as a person, not as a werewolf.