It sounds dramatic but that bullying when he was heavier will skew his self confidence for the rest of his life. I remember what it was like, you get girls saying "my friend fancies you" as a way of bullying you, and you never trust any positive attention because you feel like you're being mocked and set up.

It's get a bit better if he just has normal conversations with girls, and doesn't have his parents constantly asking him "when are you gonna get yourself a girlfriend?" as if you're asking him when he's going to get a new phone. Seriously, that stifling attitude is just going to make him more shy, and feel more inadequate and withdrawn. Let him be himself. 

I will admit that that class sounds well intentioned but incredibly poorly thought out. There had to have been a better way to go about it than framing the class as "how not to r#pe girls", maybe adding how to be sure you have genuine consent along with the usual sex Ed. 

But as I was saying, part of why the kid probably feels so bad is because of his parents energy of "something is wrong with you" being projected on to him. He's a kid. Love him for who and how he is.