Not having happened. Not a cover up for something else. Just that it didn't happen, but the US was so hard up to beat the Russians at something that they staged it.
It's ridiculous. But the world we live in is also ridiculous, and the internet has enabled idiots to meet in numbers that have never been possible before.
To cover up that the moon doesn't exist, of course.
I'm sure we can come up with a ridiculous conspiracy hypothesis around what we're actually seeing when we think we're seeing the moon. Might need to involve time travel to explain historical records.