@MrGoat Had that happen to me with the guy I was dating, and he explained he wasn't feeling aroused as such, and I understood because genitals sometimes just do their own thing in response to strong emotion.
@Nimthiriel Can confirm, wind has blown the right way a few times.
Just a human touch, a sense of longing and comforting someone in distress, it is not a crazy alien concept that he got an erection. Its quite normal and pretty logical
@MrGoat I feel bad for both of them.
I've been that guy and though the woman in question didn't notice (thank god) I was dying inside!