@Appleton-Barn0 Your lovely home is certainly desireable to various groups of guests. In your rules you state that you will not accept same sex groups unless there is a discussion with you. Presumably you had this discussion with this group and determined they would be good guests. How do you do that? Do you require previous good reviews. Was there something about the ethnicity of this group that was relevant to your negative experience since your post includes this description? Do you have more detailed house rules sent to the guests or provided at the site?
You have 45 reviews and most are positive so I wonder if you have just been lucky with the guests. I always try to find the lesson in a negative experience because that is when I learn the most! 😛
As hard as you try, it's almost impossible to avoid a bad bunch if they're clever about it. As long as they didn't cause any damage, put it down to (a bad) experience, @Appleton-Barn0.
Oh, and the same sex group 'rule' isn't enforceable (British/European law).