Friend decided to make Nether portal, Game crashes. he reloads the game and the nether has been Formed with the overworld

My friend decided to load up a world and he decided to make a nether portal. When he created it his wifi went out and he deleted the tab and went to fix his wifi, after reloading the world the Nether mixed with the Overworld. this was on a flatland on a IOS iPad. No clue, never seen this one before.