Possibly if it's nose has some "blockage" in it, it may just be breathing hard. Are you sure it sounded like a sneeze?? or was it more of a wheeze??

What are those temps? humidity? Does he spend a lot of time in the cooler side? If so, with the higher humidity and low temp of that side it could be a sign of a RI.

If you can, try to open it's mouth. Does it look like there is anything that looks like "gunk" in it? how about cottage cheese? These could be signs of RI.

If you ever see him gasping for air, or sitting mouth open. Then you should get him to the vet.

Hopes this helps!