Lol, happy farts. That's funny, but that is kinda similar to what it is, as I learned here. Male Bettas like making "bubble nests" when they are with a female for spawning (to hold the eggs), but they seem to also make them when they are content, happy and comfortable with their surroundings. They don't really pass gas to make it though.
My Betta, Speedbump, has been adding bubbles to his bubble nest and it keeps getting bigger and bigger. When the snail goes near it to clean the tank wall he gets this anxious look on his face and tries to stay close in case he needs to protect it, and if the other fish go near it he chases them away as if he is saying "Hey! I spent a long time making this. I don't want it messed up!" LOL.
Looks like your betta is a pretty happy one. :)