Do you enforce the Crit Fail misinformation on Recall Knowledge?

A Witch player ask to RK about the lowest save of a giant and crit fail.

The GM rolled in secret and told the Witch player, your character thinks that the lowest save is Fortitude.

The Witch player not believing the GM didn't cast any fortitude targeting save.

Who is right, and what would you do in this situation?

Back then my old GM tried to enforce it, the witch counters with no longer doing RK checks, in his words "guessing is better than being forced to commit"

Then the GM tried to give hero points if he does commit, which he never takes unless he has 0 points.