They're legendaries, alright. The guy hacking them in (a frenchie hosting a site at
smea's devblog) apparently only modified the wild pokemon appearance values and not the level, which is why the mega I linked to doesn't have a mega evo icon next to its name (it's level 100 though, so apparently this guy figured that part out along the way).
Gamefreak stated that they wanted to release the game fully functional and wouldn't be releasing any content patches, so its likely that everything is already hard coded into the game and just waiting to be found by this guy, OR we wait until they release a minor patch (not unlike the lumoise city fix recently) to unlock the required areas.