Thousands of tardigrades settled on the Moon, after stowing away on a space mission. They mutated due to solar radiation and reproduced. Now they roam in herds on the Moon, eating all the cheese, and plotting their glorious return to Earth.
The Truth:
There were no living tardigrades likely to be onboard. At best there were some dehydrated tardigrades in the tun state, embedded in epoxy resin, inside a disc containing an archive of humanity (See: www.archimission.org).
The total quantity would have been microscopic in size and the mass would have been far less than 1 gram.
At the time this occurred there were no regulations governing the delivery of such a low mass of non-living organic material to the Moon, which was not a protected location. No planetary protection guidelines were violated due to the extremely low mass and non-living nature of the alleged tardigrades. As there is no liquid water on the Moon, there is no way to rehydrate tardigrades on the Moon, nor could they reproduce on the Moon if there was liquid water there.
The Deeper Truth
The tardigrades were announced in the month of April. The tardigrades might have been a myth constructed as a media "beacon" to mark the location and time of a shipwreck on the Moon for future historians.