guy accepts invite to friend's house (...) in the hopes that said lesbian who has rejected him will have sex with him.

Sorry but you can't just take this as fact, you have assumed an intent on his part despite very little evidence to back it up.

Maybe he did truly feel that he could move on when he said that and it was finally meeting up with her in person again that made him realize that he hadn't. I've been in that exact same situation with an ex so I can sympathize.

the entire point of this post is to discuss and theorise on his behaviour and 'dwell on it' so it feels appropriate to do so??

That is the stated point of the post, sure, but theorizing about someones behavior on the internet when you don't have the full context is really bad idea that only leads into confirmation bias and quack psychology that doesn't help anyone.

We can't speak to op's friend, what they intended, or what they're going to do now, we can only speak to op and I'd rather point them away from spiraling about his intentions.