My betta did exactly the same, ate my snails algae wafer. I just fasted him & it soon went down. He could hardly move his stomach was huge! Now I only feed blanched veg to my snail as he doesn't touch that. He should be fine like you said fast him then once his belly has gone down I would then give a pea.
70 gallon elephant nose tank, Gonzo the elephant nose and friends!
30gallon borara merah and brigittae green, red longfin bristlenose, shrimp, ninja, taiwan,bamboo, and snails.