According to Atlasloot's tweet, the datamined Lunar Lantern and Festival Lantern will be from the in-game holiday Lunar Festival event for 50 coins of ancestry each lantern.
Last I checked on the PTR databases, the Lunar Lantern is the alliance version while the Festival Lantern is the horde version of the pet. This may have changed since then, but we'll have to wait for the holiday to come around to find out for sure. Note that both are Bind on Use, though, so it's likely that players will be able to acquire both on a single toon for their collections either way. :D How players manage to get both on one toon if there are horde and alliance versions... well that's up to each person to sort out. :P I know I'll probably need to level a horde or bug a few horde acquaintances for a pet trade!
The Lunar Festival was the last seasonal event that didn't have any companions associated with it, so with the implementation of these two pets, all holidays are covered! Yay lol. :)