From: Katherine Casey
My guess would be that the "open to" bit is intended to bring in people who might otherwise feel they're not welcome if they're not specifically invited, more than it's intended to dis-invite people who already know they're always welcome at Wikimedia events. 
From: Jeremy Baron
> I've never seen editithons that exclude people before.  I've been to a couple of black history events, and all were welcomed, although of course there was a very high proportion of African descent. I think the point was actually to be extra inclusionary: to cover all of the above not just a subset when recruiting new editors. So potential recruits don't think but I'm not really {{label}} and exclude themselves. I'm pretty sure others won't be excluded but these events will be *focused* on topics related to those groups and editors with some sort of a connection to Africa.

I think it is important to be explicit, not to be "pretty sure others won't be excluded" or "think the point is to be inclusionary". The text of the announcement seemed very clear about the subject matter and attendees. Intent isn't sufficient if the wording says otherwise.

Personally, I wouldn't have a problem with an edit group that was specifically restricted to African or Afrodescendant attendees. Yes, it is exclusionary, but there are plenty of other groups for African people to edit with. 

Alternatively, one could make the wording more inclusive, but state very clearly that the editthon subject matter will be specific to topics and biographies directly relevant to Africa and African heritage globally, now or historically, ONLY. The same is applicable to women's editathons. Without laying down some sort of fixed guidelines (either attendees, subject matter or both) it is too easy for dominant others to derail an event, even without intending to do so.

- FeralOink