Red flag is him refusing joint custody and immediately going for sole custody. An excellent parent recognizes that the children need a relationship with both parents.

Abusive people don’t look like cartoon villains, but rather like normal people. I’m not saying this guy is abusive, but posting a smiling photo of him with his kid literally proves nothing one way or the other.

Because he's an asshole, that's why. He wants to make things difficult for his ex because he's a vindictive man-child. If he was verbally abusive to her during the relationship, he'll come down even harder outside of the relationship to "make her pay."