Answer:
I has to do with the shape of the stadium.
the name came when in a meeting of NFL and AFL owners, they were trying to come up with a name for the championship game. Kansas City owner Lamar Hunt jokingly said that it should be called the "Super Bowl" because he had seen his daughter play with the "super ball" toy. when the rest thought about this, they saw how it made sense. "super" as in the biggest football championship. and "bowl" because it matched with the college championships' names. (ex. Rose Bowl). Lamar Hunt only meant this as a "stopgag" name until a better one was found. But as you can see it became permanent.