It sounded that to me too. That he assumed the issue is cleared and that he can continue conversation without worrying that she would interpret it as hitting.
Because since he now knows she has boyfriend, therefore he is not hitting, therefore logically she is unlikely to interpret further conversation as hitting. Incidentally, that is remarkably similar to the way people on spectrum "logically" interpret humans - have hard time imagine other person perspective (here he knows he is not hitting therefore she knows too) - and get into trouble despite really not having bad intentions.
I see, I was interpreting the GP comment as that the OP stopped talking altogether after knowing she had a boyfriend. But you are right, it can also be interpreted that after the OP knew she had a boyfriend he changed from "small talk" to some more interesting subjects cause he felt more at ease of not being misunderstood as hitting on her.
Because since he now knows she has boyfriend, therefore he is not hitting, therefore logically she is unlikely to interpret further conversation as hitting. Incidentally, that is remarkably similar to the way people on spectrum "logically" interpret humans - have hard time imagine other person perspective (here he knows he is not hitting therefore she knows too) - and get into trouble despite really not having bad intentions.