Yes, this is frostbite. You can't really do anything to treat it, other than make sure it doesn't start to get infected. If it DOES get infected, you're going to have to trim it off, unfortunately.

Make sure you don't put anything on it for "prevention" because it's not going to help. The best you can do is re-think your coop set up. It may be fine but no one can predict the weather...Can you build a temporarily smaller space on the inside of the coop for them to roost in? If it's too open their body heat may be too spread out to keep their waddles warm.

Poor fella! I hope he is feeling better soon. That's gotta hurt!