"Fast", to me, from a software development perspective can still be meaningful, in the sense of knowing what techniques, patterns, paths, ... enable performant execution, and providing easy and straightforward paths for the user along those. Which, ultimately, leads to high performance in most ways the user will apply the provided framework (in a more general sense of the word). Hope that makes sense.

And it must be OK to claim "fast" as a goal, from the early stages of a project, even before it may be possible to create any meaningful benchmarks. As long as it's discernable for the intended audience the precise stage of development or maturity the project is currently at. Which, I believe, the project in question is communicating just fine ("still in early development").