Unfortunately that information comes from the fact that Bettas CAN live for short times in small amounts of water (in their native lands during the dry season they often need to survive in puddles until it dries up then they flop themselves to another puddle, this is also why they have labrynth organs, so they can get air from the surface rather than relying on air in the water). But this is not a proper way to permanently keep a Betta, if you don't have room to keep them in something bigger (at least a gallon and perferable 2 gallons or more) then you shouldn't keep them. Keep in mind, the smaller the container the more often you need to do water changes. (for a gallon or below, daily water changes would be best, so it would be a lot of work).
Linda