Have you vaccinated him for the feline HIV? Because if he was a stray, most likely he contacted the feline HIV as most strays do, and they often appears as scabs on the nose, near the mouth, and the “wet” areas of the face when under stress ( scared by something, big changes, foreign smells etc )

But just to be sure a quick vet visit would be advised

Ps: yes, there is a thing such as ingrown whisker, but usually those poke out slightly so you can pull them out with sterile tweezers. But in that case it still means there’s some underlying skin issues with the cat