I've had plenty of men I've been kissing put my hand on their dick and all of them have been erect! I'd have been quite bemused by the whole thing had they not. I don't think that actually makes a difference but I'll be amazed if that bit is true.
Anyway.
I don't think it would be sexual assault in a legal situation as I can see he reasonably believed he had consent. I don't think he needs therapy. He needs a good talking to about what's acceptable though.
Why do so many men think that as soon as you're happy to kiss them you're happy to start touching or shagging them?
I think for most women kissing is a separate and exciting stage and I hate how many want to rush past it. Kissing is fun but often ruined by having to repeatedly move hands away or push them back or explain why you don't want to start riding them on a dance floor.
I remember once after a series of unsuccessful online dates with men like this, one man kissed me, pulled away and said goodnight with the sexiest smile I've ever seen. It was pretty incredible to 20 year old me that he had simply kissed me without trying to finger me next to the night bus. Instant turn on.
Next, I've always found the grabbing your hand to put it there quite sexually aggressive anyway. I know lots of PPs are saying that she wouldn't have his consent to touch him so it's the same. I still think it's better for people to move their own hands but SLOWLY.
Kissing someone and suddenly there's this hand pawing at your breast like they're trying to milk a goat is annoying. Kissing someone whose hands are on your waist and then they very slowly move up your body and wait a moment before they get there to see what you do before touching is hot. At that moment, someone who wants you to carry on will deepen the kiss, arch their back, move their body closer to yours etc. It's really quite hard to misinterpret.
It's the same as any next step. Go slowly, hover nearby and see how they respond. By the time you're groping at someone's genitals they should be so obviously aroused and absolutely desperate to be touched that it is obvious through their body language and words.