What did this "sneeze" sound/look like? Snakes don't have diaphragms, so I'm having a hard time picturing what happened.
Monitor your animal in the meantime for any other symptoms of respiratory illness; mucus and/or bubbles at the mouth/nose, star gazing (extended sessions of periscoping upwards or propping the head/neck up to appear gazing at the cage top), wheezing noises, labored breathing, and food refusal can all present with RI. Research accredited reptile vets in the area in advance.
Also, I have to say; going to a reptile rescue and then heading home and interacting with your own reptile without changing clothes or cleaning up was putting your animal at a huge risk. Even if it's highly unlikely he would catch something and start presenting symptoms the same day as exposure, it doesn't change the fact that he WAS exposed to all sorts of nasty pathogens and that he may very well end up infected with something gross. If you're going to interact with sick reptiles or reptiles you arent 100% positive are healthy (even if you think they are) then you NEED to take the necessary precautions to keep your own collection safe and that means changing clothes in a separate room from your reptiles and taking a shower before you interact with your own animals. Reptile rescues are great but they tend to be full of mites and disease and you need to make sure you don't transfer nasties from yourself to your animals.