Hey yeah I saw this too! I thought it was only directed to one individual, but wow, there ya go.
Yeah it doesn't make much sense to me the whole you can only train with us if you're one of us thing... I've enquired once to a large Goju ryu organisation just in participating in an online session, and I got a similar response, only members.
Yet I've also encountered many groups that are so incredibly welcoming and one recently let me come to a private seminar they held with Hanshi Tino Ceberano.
I definitely prefer the open and sharing attitude, all part of the one family. The only reason I can think is that a non-member may take away the spot of a member and they'd miss out. So I understand that view I guess. But yeah, don't know.