Yes, here we have a problem.

You have a case of very deadly F’ed up faces.

That happens by accident a lot of the time. You make a selection and without realizing it you select vertices on the back and move stuff around and without you know you’re moving stuff you don’t want to move. Then you see something like that and you’re like what the hell happened. It happens to us all.
Or maybe you made an inset faces and it went pass the desired amount.