Yep, he does have a psychological disorder. I just remember one of the chapter of his book. Instead he help the kid, he stayed with the kid which lock them both in the basement while everybody look for them. When he was asked why he didn't help the kid to get out the cage. He said - I did help, I accompany him inside.
That's his father's fault. He used that as methode to punish Grayson as a kid.
So he learned to wait until the punishment ends or you receive even more punishment.
He even remained when they got the kid out, so he could tell the father (who locke the kid up) that it wasn't the kids fault that he is gone, so the kid wouldn't receive more punishment.

The novel clarified later that Grayson just lied to him since Chase (and in general, dominant alphas have foggy memories during their rut) didn’t remember anything at all after sleeping with Josh, and Grayson LOVES fooling around with people, so as soon Chase saw the dog, he passed out; of course his trauma grew worse because of this.
On the other hand, Grayson keeps reminding him of that day but in reality when he mentions a dog he is just referring to Josh lol.