> shouldn't need a medical background to know that having something press on a spot for a couple of hours will leave a depression in your skin
I read “soft tissue on top of” the skull to mean more than a superficial skin depression.
We have layers of connective tissue between the skin and skull [1]. Their damage usually calls for medical attention.
What he's saying though is that the original poster is vastly overstating the effect the headphone had on his head. There was no dent in his skull, just skin deformation that happens with literally every headphone.