I would imagine their intelligence is directly proportional to the so many degrees of freedom the arms have for grasping, but don't ask which one came first, chicken or egg?
- snakes have a high number of degrees of freedom but aren't especially bright
- squid have 2 more limbs than octopuses and aren't as smart
I think the shallow-water vs deep-water thing mentioned in the article is important; reef and similar environments give a lot more opportunities for smart camouflage, complex navigation, tool-use opportunities etc than the open ocean.