Any explanation for his way of thinking??

It's the way they were raised I believe

Someone else said it’s cuz how he was raised, but I also interpreted his character as being either autistic or ASPD or similar due to the black and white literal thinking and difficulty relating to others. He has feelings but they seem to either be slow to catch on or he doesn’t display much when uninterested.

There are two reasons. 1) He is genuinely neurodivergent. Contrary to what many here say—calling him stupid—Grayson is actually quite intelligent. He even holds a law degree, though he doesn't practice. The issue is that he has alexithymia (meaning he cannot understand his own emotions). Consequently, he was taught to feign normalcy by mimicking others' reactions—such as smiling in various situations to appear less odd—though in some contexts, this actually comes across as even stranger! So, he tries to navigate society based on logic rather than emotion. 2) His upbringing didn't help him understand his condition or how to manage it properly. Ash, Grayson's father, believed he was incapable of feeling emotions at all, rather than realizing he felt them but struggled to comprehend them. So, he "raised" him using harsh punishments—like locking him in a room—and demanded almost blind obedience, threatening even worse consequences if he disobeyed. In Grayson's mind, he believes that if he frees the child, the subsequent punishment will be worse; and since he used to wish someone had been with him during his own punishments, he thinks he is helping the child by staying with them. Ultimately, he doesn't realize that he himself was a victim of child abuse, and he acts according to this distorted logic. He also fails to recognize that Santiago's father is committing abuse as well.

So this may not be the author’s actual intent, but he reads to me as autistic. With the most recent chapters,

SPOILERS:

-
-
-
-
-

How he joins the kid instead of getting him out reads to me as misreading what would be expected socially in that situation. He’s told being good would be listening to your parents and applies that without a second thought like he’s following a rule, rather than following an instinct.

Oh... I also forgot to mention that Grayson was taught by Ash—and people Ash hired—to fake and mimic expressions, so many of the looks on his face are actually false emotions he copied. At one point in the story, he even starts imitating certain mannerisms of Dane's, like tapping his foot on the ground.