Would this bother you?

My boyfriend has a female friend. He wasn’t interested In the friend, he was interested in her mother. The friend was fine with it. He said that he made it known to her mother that he was pursuing her and she found it to be extremely inappropriate and obviously turned him down. He’s 20, same age as her daughter. My boyfriend still continued to joke about how his friend is his stepdaughter. This was BEFORE we got together. But even now that we’re together, he still refers to his friend as his stepdaughter whenever he mentions her and although I trust him, it’s incredibly annoying. I laughed it off at first but I’ve had enough. Maybe I’m thinking too much about it. Would this bug anybody else?