But octopi have a breed-once-LOTS-then-die reproductive pattern, so transmitting culture between the generations would be difficult...
Maybe you get a mutation where that isn't the case and the necessary greater brain development. Or if you want to go in an ASB direction they somehow evolve to have genetic memory but at that point you're wandering into a really weird fantasy setting or something that could be the start of a cheesy (or awesome) horror story.