They are comfortable in small bowls as their natural habitat is puddles and small ponds.
This is a HUGE myth. Bettas live in rice patties. If you've ever seen a picture rice patties don't have small puddles, they are flooded! Tons and tons of room for them to swim. However their gills have adapted to allow them to survive during the short periods when the patties are drained. Just because they can survive doesn't mean that is how they should always live. I would sugggest getting your betta something larger, they really need at least a gallon. A 1 gallon tank with a light and fliter runs around $12 at Petsmart.