I used to believe that fly fishing was exactly as how it was shown on SpongeBob (fishing from an airplane), and even recall reading articles about it. I thought the joke was that they were fishing the sapient fishes of Bikini Bottom, not a play on words.
A childhood belief about cartoons

others believed things like this
- When i was a kid, i thought that nematodes would eat our house like in one episode of SpongeBobAnon
- I thought Spongebob Squarepants was a piece of Swiss cheese.— Melanie
- I used to think that Spongebob took place on LAND.— Eeveelover8632
- few years ago, finally I found out that asparagus are not big sea fishes.. — nixass
- i used to believe i was spongebob squarepants in a previous life.— former sponge
- I thought Hurricane Dennis (in 2005) and the character Dennis from the Spongebob movie were related somehow.Anon