[Open] - Friends only party switches to Open for everyone

@smoothPEACHES  While hosting a party,you have an option to select if the party should be available for only friends or for everyone.The option is in the form of a slider (Just like the way we decide the paint for a specific wall or an entire room).You'll find that option after you have selected your party type.
If you're saying that random people are attending the party in spite of configuring the party setting to only friends,then it might be a bug.