Yup he looks stuck alright. They also inflate their bodies to stop you from getting them out. I don't know what you can do but wait, or try and force him off of there. That may end up hurting him though. I would turn out all the lights and leave the room for a few more hours to see if he cant get himself off when he feels safe. Or else it looks like your going to have to either pull off the thermometer or find someway to get him off.

Oh, he's not constricting it from the looks of it. Just stuck.