head canon, drug reference, believe it or not I'm currently sober
Spongebob and the rest of Bikini Bottom's population feature in a show about the ocean, frequently watched by stoners.
Captain Horatio Crunch is the sea-going mascot for a delicious cereal frequently eaten while stoned.
Therefore, Cap'n Crunch knows of Bikini Bottom's existence and has probably interacted with Mr. Crabs at least.