What if time travelers did show up, but only in any of the multiverses except this one? What if all of the time travelers turn out to be multiverse versions of Professor Hawking himself?
By telling publicly about the party he could have also forked the time continuum in two. In one of them the future time travel inventor reads about the failed party and abandons studying physics, while in the other one he doesn't, and we should reach the second continuum's HN to know what happened.