Not bumblefoot. It looks like he lost the ends of his toes, probably to frostbite. Wash them well and keep them clean, they will heal. If you have Blu Kote, spray them to prevent infection.
I've been washing and applying Blu Kote as needed and already one of his feet is almost normal. On his left foot, his middle toe is still pretty swollen. He his right foot has no claws and only three on his left. Poor guy!