Actually it was the GF who got dressed first.
She answered the door while he was getting dressed. He overheard a conversation long enough to know he was "whiny". His girlfriend apparently didn't believe he was dangerous or feel threatened. Not really that smart to answer the door under those circumstances, but the OP and his girlfriend knew who it was before they opened the door and that enough was not enough to make them feel threatened.
I wasn't there, but if OP ever had to explain it to a jury, this isn't going to make sense to them.