Does he say no because he doesn’t feel it? Or he doesn’t want to believe it? Why would he deny something as tiny and clear cut as a point in a game? A game, by the way, that is rigged to get him what he wants.
But – there are many inferences one could make about his personality based on the reason for this no. It could simply be that he does not like to lose. There are people who could not bear to concede a single point in a single game. Maybe Laertes is built like that? Or he’s so hyped up on adrenaline he can’t feel physical contact. That would reveal something about how he relates to his body.
Or, he doesn’t mean to deny the point – he just really can’t believe Hamlet has enough skill to win it.
Or – it’s an attempt at humor.
Or or or or.
There are a lot of possibilities in a no.