Their post actually drew a lot of positive attention, and people seemed excited to learn about Hugh Jackman’s return. We didn’t really see any traces of negativity in those remarks before the post went down, so at least the impact of this leak wouldn’t have been negative for Fox in any way.
We don’t know why the studio hasn’t confirmed the actor’s involvement officially yet, but they probably have a good reason, and we would expect that the “big word” is coming at some point soon anyway. With all of these leaks occurring periodically, Fox might as well draw some attention to themselves on the official front and tell their fans what’s going on.
On the other hand, it may simply be too early for them to speak about the film yet, and in any case they have probably prepared their official announcements very carefully and are sticking to a schedule. Are we going to get a confirmation about Hugh Jackman’s involvement anytime soon? It’s hard to tell – but fans are certainly hopeful, from what it seems.