Sometimes weird eggs just happen. I wouldn't worry about it unless it becomes consistent or worse or the hen displays odd behavior. Of course, a side of oyster shell in their pen is never a bad idea--if they need it, they'll eat it; if not, they'll ignore it.
I have a hen who consistently lays a lopsided egg, and she's one of my best layers--just something inside her makes those eggs wonky. She acts normal like all the rest and has been laying like that for several months, so I'm not worried.
However, do make sure they are getting a balanced diet (layer pellets such as Purina Layena plus a side of oyster shell and plenty of forage if possible--supplementary greens if not), and just keep your eye on it. Good luck!