Another guess: He actually said it and a few people heard it, but when he said it was before everything in the universe was constantly being recorded, photographed, and pushed to the internet, so there's not necessarily a record of it.

Back then, you could just deny something happened, and often get away with it because you weren't being surveilled 24 hours a day.

It's like when someone very knowledgeable about a subject posts information on Wikipedia. Even if they were there first hand; even if they were personally involved with the event; even if they wrote magazine articles about it and did radio interviews about it, and it was covered by television — if it happened before 2000, it'll get erased from Wikipedia by someone on the other side of the planet because there's not a web link or an ancient library book to cite for "proof."

/Yes, I'm speaking from experience.