Sounds to me as if your dog may have traumatized that part of his nose. It's not uncommon for dogs (who always lead with their noses) to go sticking their snouts into long grasses or branches and causing small abrasions either in the nose itself or around the outside edge.
Add to that the fact that dogs tend to get things stuck in their noses (like foxtails), and you've got a recipe for nasal irritation.
The good news is that your dog isn't acting like he has something stuck in his nose. The fact he's not sneezing or pawing at the nose tells me that there's nothing there really irritating the area...it's most likely that he just got a little abrasion in there.
Your vet will give you a better idea of what is going on...however, I don't think I'd fret about it too much today.
I hope this helps.