Bizarre!
If it was a roommate, shouldn't they roommates just have discussed the party? Quite strange for the landlord to get involved (regardless of being family!).
I hope your friend at least met a lovely lady!!!
Reminds me of the early days living in Melbourne, in a private rental (bungalow). Came home one day to find the house unlocked and my tv on.
I went to the house at the front where my landlord lived and asked them to go in as I was scared.
His response? You're never home anyway, you probably left everything unlocked.... I was an 18 year old girl, living alone and one of the doors I never used as it was a shared deck with the main house and had to be unlocked from the inside.
His two sons were aged 17 and 23 or so, I think he was letting them chill out in my place when I was out. I moved out the next weekend.