I love this - "it's just engineering" say the people that think the hardest part about building a spaceship is having the big idea to build the spaceship. Note the "I love this" was sarcasm.
My point was that the architecture they are using has already been done multiple times for graph databases using things like RDMA (which has existed in HPC for ages), that is a known quantity. It was less "it's just engineering" and more I've seen similar implementations for a long time so what makes this different? I am interested in this space in part because I spent much of my time in HPC working on graph databases.
You should quickly skim sections marked with a (comically fat) "!" symbol. These indicate their "key design choices and insights" in the design space.