Octopuses are actually exactly what I was referring to when I said aquatic animals didn't teach their young, which I guess was unclear. In most octopus species, the male dies after mating and the female tends to the eggs, before dying when they hatch. As a result, without a major change in the octopus life cycle, it is impossible for knowledge to be passed down between generations like they are in humans or even animals like chimpanzees or crows.
Such changes do happen; it can be seen in viviparous sharks and snakes and in non-metamorphic frogs. But there are clear evolutionary incentives for the status quo. Part of the reason for this is simply that octopus young are extremely small and numerous, so there is little incentive for the parents to take care of them once they disperse. But even if they did not, the adult octopus is also vulnerable to larger predators, which would cause knowledge loss and thus reduce the incentive to pass down knowledge.
While it is certainly not impossible that under the right conditions, they would have developed intelligence, you have to also recognize that they face all sorts of evolutionary obstacles to developing intelligence that terrestrial animals do not face. And while these obstacles can certainly be overcome, if we assume that alien life is at least vaguely reminiscent of earth life, we would come to the conclusion that intelligence should at least be much more common in terrestrial animals than sea animals.