I would guess a stuck shed, I got my female lesser pastel this last Tuesday, when I took her out of the bag she was sweet as can be, balled up checking things out with her head probably cuz she was new tot he environment. later that night I took her out again and ugraded to a better size hide for her, she was way nasty, striking at me non stop. I put the hide in threw some humidity in her enclosure and left her alone, I got up this morning to find a small dime size piece of shed with an eye cap on it. I left her alone all day today, im assuming with her being new to the environment and having gone through a bad shed that she was temperamental.

I would guess stuck shed mainly because when you buy a snake from a breeder chances are the breeder has 100's of snakes that they are trying to get rid of (especially this time of year before it gets cold) and with 100 babies and trying to flip them there is no way you can spend individual attention to every single one of them. and tbh if you aren't taking a ton of time its very easy to overlook a piece of stuck shed. ive missed small pieces myself that I didn't notice till it came off a few days later and im only working with 10 snakes!

the side of their heads and small part of their necks seem to be where they are the driest for whatever reason. I wouldn't worry about it too much, you have a shed box it sounds like and water, he will be fine.