Here’s what was mentioned on the official Pokémon GO Facebook page on the matter:
“A few of our Legendary Pokémon had erroneously been granted to some Trainers. Thanks to the help of several of our Trainers, we were able to locate them and bring them home safely.”
In other news, Pokémon GO has launched in Mexico and Brazil. The Battery Saver mode has also been removed from iOS as users were experiencing it to be buggy, but Niantic is confident that a fix for this should roll out within the next several days.
Pokémon GO is available on Android and iOS.