I am not sure that there is such a thing as a 'non public' meeting any more.
At one time, the group study, because it was held in a private home, was classed as a 'non public' meeting. Disfellowshipped persons could always attend meetings at the Kingdom Hall but were not allowed in to the group study. With no group study any more, that issue has gone away.
I am not a legal person but my guess is that as the congregation displays the days and times of the meetings outside the Kingdom Hall, often with the message 'all welcome', then it would go totally against their charitable status to refuse entry to people of the grounds of ethnicity, race, religious views or sexual orientation. What they are clever at is sitting disfellowshipped people at the back and totally treating them as if they aren't there.