Please don't lecture me on how Science develops. I am aware. Sure each discovery builds on another. But also each discovery also can be impacted by random chance, not to mention lost, and rediscovered. Which means it isn't just a hierarchy.
Not to mention Cephalopods science would have different starting point, perspectives, senses, etc. So you get a completely unique "tech tree".
It was an outlandish idea, but this is GRRLPOWER. Everything is magic.
For real, but a Hypothetical Real Earth Cephalopod could have discovered a material stong enough to fit the bill. And a way to make something synthesize it. And a way to grow a structure out of it, that they can expand upon.