If you can use the side of a pen (as if it was a speculum) to gently open the snakes mouth, look inside at the back of the throat. If it's full of flem, it's early stages of RI and should be treated immediately. If it's not full of flem, it could be some retained shed inside it's nostril and will come off/out in time.

If the temps in the enclosure are not warm enough, too damp, too dry, etc. the snake could get an RI without exposure to other snakes. You could also carry RI (like spreading the flu on your hand) from someone elses snake to yours.

Based on your description and the time of year, I would check for flem buildup and nip this in the bud before it gets worse if you find flem.

Rick