You're also supposed to hate him in that period. It's actually the one moment in the whole game where you're actually afraid for him. When he gets sick you know he's not going to die, because they wouldn't just kill him off. That moment is primarily about Kratos being held accountable for how he's raised him up till then. And him needing to make some sort of peace with his past in order to save his son. But when he starts to become this little bastard is when he feels much more at risk of Kratos (and the player) losing him.I know there are some people that don't like Atreus due to his little ''episode'' which always struck me as weird. The kid's got a bad attitude for perhaps five whole minutes before turning into a sweetheart again.
It also makes sense for Atreus to assume his father was acting like an asshole and treating the problems of others as beneath him because he's a god and therefor better than everyone else, prompting him to do the same especially following their moments of bonding. When actually Kratos doesn't want to bother with anyone and wants to be left alone because of his lifetime of being a god and how much he hated it. But because he refuses to open up to his son he's again leading him down a dangerous path.
I really love Atreus' shitheel phase, though I do feel it ends a bit abrupt. I think it would've been better if they'd used Kratos' past ghosts in Helheim to shock Atreus out of this mindset. As if to say 'yeah, this is where your current path is leading you to'.