"I guarantee, that most fish swim in an are(sic) bigger than a foot or two.."
Don't guarantee something you can't deliver on. Most reef fish, in fact, spend all of their lives in very small spaces among the reef... Small reef fish can spend all of their lives in a few square feet. I've taken scuba trips where certain damsels amd other fish are known specifically by the dive instructors.
An octopus is an aggressive predator. They wander the reef looking for food. They travel everywhere looking for food.
Someone said his spent all of its time in one place... does that strike anyone as natural behavior for a predator?