I think there might be some what of a mixup in translation, but those people at the beach probally panicted, hence the stoning. Aside from that, they suck! Humbolts attack, alledgedley (sp?), anything that it might be able to eat. The story gives bare bones account of the incident. I'd like to read more detailed accounts, before passing judgement. But fact still stands that they suck!
One thing to keep in mind: I worked in seafood previously as a cook and often distributors would refer to squid as cuttlefish and vice versa; most of the other chefs I worked with didn't think there was any difference based on this fact, even after my attempts at education. In certain foreign languages, particularly latin/romance languages, the two terms are blurred constantly in literature. Maybe not in scientific literature, but by the everyday lay person absolutely. I remember reading a translation of Twenty Thousand Leagues Under the Sea when I was a child and being shocked to learn that the giant squid was actually either giant polyps or giant cuttlefish. I also seem to remember a 17th Century description of "an immense Sea-Cuttle" that was undoubtedly an archituethis. I believe this was the Dingle I-Cosh Squid.
Perhaps it was at the end of its lifespan. How do you stone something in the water??? Maybe they killed it some other way and "stoning" is how it translated (strangled, beat it with their fists?). Or else it was almost dead and they only thought they killed it.