What in god's name was this octopus trying to do?

Maybe that's the wrong question. There's no question that octopi are smart -- they can puzzle their way through surprisingly complex tasks -- but they're also not a lot like humans. There's only a limited extent that we can empathize with animals -- and there's a good chance that we'll get it wrong. (c.f. http://goo.gl/D8yjd)

Octopi, though. Octopi are particularly difficult, and I don't know if "volition" is really the right model to describe what this animal is trying to do.

Most of an octopus' neurons are in its arms. The rest are in a donut-shaped brain that surrounds its digestive tract. Vision and hearing are handled centrally, but proprioception, smell, touch, and taste are mostly delegated to the nerve cords in the arms. Which means that, subjectively, an octopus is probably something like an unruly parliament of snakes ruled by a dog. 

If you've ever gotten a chance to interact with an octopus in person, you'll find that it really doesn't have much control over the details of what its tentacles do. Run your finger over the sensory surface, and its suckers will cup your fingers and the end will curl around it. Only afterward -- when the octopus actually looks at what you're doing -- does the octopus seem to get a grip on what its tentacle is gripping. 

This octopus is crawling out of its tank. But it probably doesn't have a great idea about where the tips of its tentacles are, and -- because it can't see what its arms are doing -- probably doesn't yet know that it's trying to make a break for freedom.