With Lost they repeatedly said that nobody, not a single person, had guessed what the ending was, not realizing that this was one of the first shows to go massive for fan theories on the Internet so everything even remotely plausable had been guessed.

So yeah, they painted themselves into that corner fair and square as it was clear they had no fucking clue what the ending was when they started that show.

If it was me, I would have admitted someone guessed it and just picked whichever fan theory seemed the most sensible to me.