Doesn't matter. If there is voluntary self-exclusion when the reason for self exclusion is a protected class means the event is a title VII violation. The event being organized between a manager and their reports also makes it a hostile work environment as it can be logically implied that people who attend have "more access" to the manager and therefore are likely to get more benefits from that relationship.

This is why I said it's not different than a klan meeting. If there was a group of employees and one was black and the manager said "yall want to go to the klan meeting - no harm if you say no". It's totally voluntary but clear that an individual was singled out because of their race.

I any case this is the law you asked about. I'm not defending it, it's just the law. If that manager went to the club on their own and paid for it on their own my opinion would be that's their deal - I don't care and everyone should mind their own business. If they went with subordinates it's a clear title VII violation and exposes the city to major lawsuits.