the largest octopi are something like 8-10 feet stretched out from tentacle tip to tentacle tip, whereas the giant squid can be over 40 feet from the crest of its head to the end of its two long tentacles. Squid also have cartalege structure in their body, while octopi are lacking in any solid structural internals. You could take an octopus like the one in that video and cram it into a small fishbowl like stuffing a sleeping bag, and it would be just fine.