From my recollection i don’t think the article tackles an answer for that. But it does say that as far as the octopus goes its likely a learned behavior as older octopus are the ones involved in this, and younger ones don’t or if they do they seem to struggle. So it’s probably a combination of incidental interactions with other fish where various parties happened to be in the same place and benefitted from ganging up on prey, and slowly learned to cooperate 
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