[nabla9]

Most likely because they have complex tentacles that need fine motor control. Their brains developed to control their body. Their eyes seem to be good as well.

Even in human brain huge area of brain dedicated into hands. Human fine motor skill (or dexterity) is superior compared to other apes. We can do small detailed moves. Other apes and monkeys are clumsy.

After the complexity of brain developed to control their dexterity, octopus gets benefit from spatiotemporal intelligence to exploit tentacles in hunting and moving. It's not surprising that intelligence plan and solve problems as well.

[iguy]

I guess that's it. Some other asocial animals are pretty smart, because they need it for hunting, or something. (Although even the most anti-social mammals still interact with their mom!)