First thing always with burns — irrespective of source or cause — is to get them properly medically treated. Do not risk infection because infection is no joke.
Speculating on the cause of the burn? I’m not sure that’s too helpful — the pictures could depict burns from a thousand different sources. Main thing is to get it treated immediately.
I’d avoid attributing lurid explanations to this: it could be as simple as an electric blanket malfunctioning, or something similar. Just get it treated.
One other thought. I’m sorry that this thread has attracted so many sillybuggers and know-it-alls. I hope your boy is OK — your doctor will have a better idea what caused his injuries than any of us here. Cheers, mate!