A dogs nose is dry when they are inactive for awhile. This may have fueled the myth that it means a dog is sick because if your not feeling well you're not active and so the nose is often dry when ill unless producing mucus of course (which REALLY means your dog is ill if they have snot). So, watch what happens after you play for awhile or when it's usually warm. I live in the desert so in the summer dogs noses drip a lot (clear normal fluid) because it's very hot. When we were kids my sister and I made up the name snobber for it since it's not snot and not slobber, just a drip because it's very warm. ;-)
A dog's nose is usually moist. If it is dry, may be due to environment. Don't worry unless your dog shows other signs of being ill. He may just have a dry nose from breathing through it and should go back to normal when awake. Much like we get dry throat when we sleep