Weird... it is definitely possible he was passing gas through the other end though as BPs are known to fart with their mouths open... for some reason.

I once encountered something similar to what you described with my BP, heard him making sounds like "ack ack ack" (except without the vowel sound) after feeding one night and saw him sort of rearing his head up and down with his mouth open in his hide. I lifted his hide to look and found that he had a small wood chip stuck in his mouth next to his glottis. As I was looking, the wood chip fell out and my BP went back to normal. Not sure if something like that might have happened with your snake?