Or maybe they are still down there.
Lurking.
Waiting.
Plotting.
Or, also possible, someone found a fossil beak and compared it to the size of a beak from a regular octopus and went "Yikes! Here be BIG monsters."
Ether way the octopus is a freaky deeky beast and they creep me out.
Could be true! Lots down in the ocean depths we know nothing about.