Though, to be fair, Wolfram did run a previous prize contest about a conjecture that he had thought about but not solved, and someone else successfully solved it:
And that was all about proving that Rule 110 was capable of universal computation. (They first found a way to map Rule 110 to the tag system put forth in that prize.)
This zoo of 3-predecessor cellular automata is an impressive lot.
This zoo of 3-predecessor cellular automata is an impressive lot.