An "announcement" on Facebook does not equal making a public announcement.
Isn't that obvious? It seems so to me, but not to an increasing number of organisations and event organisers. One particular one has been frustrating me recently.
If you do not wish to be used (sic) by Facebook then most of the links to these "public announcements" do not work or you get a tantalising first line if you're lucky.
Of course this is a strategy used by Facebook to encourage more people to engage in its spying programme (see posts passim), but it is supremely annoying when this is information that you need and some berk has put it onto a closed website.
Oh, and then they no longer bother to put it onto their own website because "it's on Facebook".