Yes, from what you described they are definitely stress marks. I wouldn't worry too much since he is still new to his environment. Him not wanting to get back in his enclosure is probably due to him wanting to spend time out exploring with you.
I would feel more comfortable knowing that everything with his set up is okay. So, if you could just answer a few questions...we can make sure that he is good to go!
What
Brand and
Type UVB are you using? Fluorescent tube, compact, coil or MVB?
What
Type and
Watt basking bulb?
What size enclosure?
What are the temps both
Basking and
Coolside?
How are you measuring your temps? digital thermometer with wire and probe, stick on, dial temp gun?
What substrate are you using?
What are you feeding and how often?
Are you using
Calcium and
Multivitamins? How often?
Are you
bathing/soaking your beardie?