Parrots dream too, including wild ones. While I appreciate the need for scientific rigour, I'd be more surprised if octopuses didn't dream at all, considering their capacity for intelligence that's already been shown.
It’s one thing to believe that other vertebrates dream. There is a clear evolutionary link between them and us. Octopus, as mollusks, are very far away on the evolutionary tree. When our lineages split, brains were rudimentary, if they existed at all. If we assume some kind of intelligence in an octopus, is there any reason to assume that it works like ours does? Do they need dreams? Are dreams inherent in any intelligent being or are they a function of how our particular brains operate. I don’t think that that is a settled question.
> Octopus, as mollusks, are very far away on the evolutionary tree.
Yes, but for some fast, short, rough guesses, regard intelligence as thinking that yields advantages in surviving in the real world. Then guess that in general intelligence is a source of effective response to the real world. Then, whatever the size of the evolutionary and/or genetic tree, notice that we are all in the same real world. So, all of our examples of intelligence are effective responses to the same real world and, thus, the many examples might have a lot in common.