I recognize at least some of the names on the attendance list there as people who don't, to the best of my knowledge, identify as being of African descent, so it doesn't appear to have been an event that excluded anyone. 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. The phrasing might be a bit awkward, but most ways I can think of to express "...and seriously, we would very much like those of African descent to fully participate at and feel comfortable in this workshop" suffer from one tonal weakness or another. At the end of the day, I can't say I resent specifically inviting racial minorities to events any more than I would resent specifically inviting women to events; given our demographics, it's probably better to err on the side of not making minorities feel marginalized or like they're being treated like tokens, than it is to err on the side of making sure white males don't feel like there might be a space where they're not the center of things.