The (19M) Girlfriend (18F) Informed her Family The Size Of My Penis

I was visiting the girlfriend at her parents' house while she was home from university. I was playing a board game when her younger sister (13) tells the room of ~10 people that my girlfriend a new drunken rant about men measuring there members and also the size of my penis. I was very taken back that her whole family members was aware of this and very embarrassed too. My sweetheart knows I' m uncomfortable being so open with people other than her on this subject. I find it especially strange that this was a conversation along with her family (however I' m aware that they are quite open). She leaves the bedroom to go upstairs as she was upset at her sister for mentioning this, however , she was the individual to tell her family in the first place. I was sat in the kitchen using the rest of the family feeling quite uncomfortable before eventually going to find her. She has been crying, assuming I was likely to be mad at the girl. I didn' t make her feel worse, however it did make me upset that will she would break my believe in like this. Advice?