I agree with CW. He never came across to me that way. His anger was directed towards Zio. After all, he just wanted revenge.
Besides, speaking from experience, having a friend, or family in his case, be killed and being powerless to do anything to save them can affect people differently. Some will wish only for revenge as he does and others may simply go borderline mad with a hate filled rage they use to cope with the trauma of the loss. The list goes on.
But obviously in context of the game, a vengeful Gryz is easier to portray than the latter of the aforementioned. That usually ends up turning into some angsty whiner.
