That wrong, Roswell admits to you that he was trying to annoy tyson from the start and thats why he was repeatedly calling tyson just a happy puppy. He then pretends that he did nothing wrong and just called him a canine (shown on day 8 on any route pretty sure).
Also have you gone through Roswells route because you seemed to have missed the times Tyson says he'll try to get on with the others and tries such as after Dave saves Roswell, Tyson tries to chear him up by making waffles and trying to stop them worrying. Simply saying he didn't say sorry so everything thing he does and tries to do can be compleatly ignored and thats fine I can't agree with. Words are cheep and actions speak louder, an empty sorry after the fact it worthless.