Is your boa going into it's shed cycle?
What color was the mucus?
Did you open his mouth to check for "excess mucus"?
Can you "feel" a "rattling" in his lungs when he breaths?
Had your boa drank water just before you took him out?
Has he been exposed to any other boas?
Sometimes when a boa is going into shed cycle it will appear to have mucus/moisture coming from their nostrols. This doesn't mean they have an RI. For "some" boas this is normal.
The color of the mucus matters. A clear mucus is the beginning of an infection, "if" it's actually mucus your seeing. It could also be that your boa is starting a shed cycle. A cloudy creamy colored mucus is a sign of an advanced RI. If your boa has this color you should have taken him to the vet yesterday!! Mucus is thick and sticky reguardless of color. If it's not thick and sticky it might not be mucus.
If you're not 100% sure of what you saw... Check inside his mouth. A boa with a RI will have thick mucus inside his mouth and sometimes coming out of their breathing tube. I forget what it's called, but you know what I mean. If you can clearly see mucus in his mouth... TAKE HIM TO THE VET!!
Sometimes you don't see mucus at all with an RI. Sometimes you simply "feel" a rattle in their lungs. If he has a rattle he has an RI and need to see a vet. BTW a rattle is a sign of a more advanced infection.
If your boa has a clear liquid coming out if his nose and it's not thick and/or sticky... It could be he recently drank water. Then you handling him caused him to regurge a bit of it and it simply came out of his nose. That's why it's important to check the mucus to see if it's thick and sticky.
Boas normally don't get sick. There's basically only a few ways for them to actually get sick. Exposure to another boa that's sick. Stress during breeding season can cause and RI. Being very cold for an extended period of time. It's summer, so you shouldn't have to worry about this one. Unless he got sick during the winter and you didn't notice. Unfortunately...... The #1 reason a boa gets sick is......
Poor husbandry. Sorry, there's really not a nice way to put that one.
So only you know if your boa's been exposed to an illness, stress from breeding or gotten very cold. Only you know the type of care he gets.
So, double check your boa. Determine if he's sick. If you have any doubts... TAKE HIM TO A VET!
BTW if you've never taken him to a vet..... It's always a good idea to take a pet boa to the vet for a well snake check up. That way you get to know the vet and the vet gets to check your snake over. If he's healthy it's pretty cheap for an office visit. If he's sick.... you just might save his life by taking him in.
Good luck and let us know how it goes.