No need to describe your taste issue. Blood, licking an iron pipe, eating steel, tingling and stabbing pains on the tongue, all sound about normal after radiation. Some Chemo patients have also reported some of this for a short time after chemotherapy ends but it seems more common in radiotherapy.
Magic Mouthwash (doctor prescribed) usually with Lidocaine seems to help folks. I chewed cinnamon Dentine gum or sucked on Altoids (strong as they are) and sipped cold water to fight metal mouth.
Radiation can and often does cause neuropathy of the taste buds. The good news is that it goes away in time. There is healing time from injuries, then there is healing time from radiation. Radiation healing time can literally be years.
Probably in another year or so he won’t notice this taste so much if at all. Keep in mind our view is much better from this the green side of the grass.