Maybe this one specific behaviour doesn't convince you of intelligence, but squids, octopi, and cuttlefish are among the most intelligent cephalopods, which are in turn the most intelligent known invertebrates.

Oh, I'm well aware of their prowess, it's been taped and discussed (also many more animals have more cognitive abilities than were thought before). I was just discussing this particular reflex/behavior.

Is this worth eating or fighting (for) it?

I have no knowledge on how they identify/distinguish food over a rock, if the tentacles have some sort of receptors on them, but apparently this didn't "taste" like food, thus unworthy of eating or fighting for and therefore better safe than sorry.

Maybe something on the surface didn't mesh well with the succion-cups

I don't know if this is true. Most simple animals are very curious.

If it doesn't move => go check it out.

well, the squid do check it out but it didn't like what he found