Are you maybe confusing “downstream” with “mainstream”? Being “downstream” of a product means that you are a derivative of that product (your upstream), taking in basically all of their code and adding your own on top.
So the meaning of downstream is different for SuperSQL (the direct derivative) and TodoApp (the commercial product)?
Imho, downstream are all consumers/users of that product. I guess it's arguable how a package manager positions in that terminology.
Edit: Also I originally said, "it was the thing used downstream", which just is to describe the consumers. Also not sure what I got into, because the original question is wildly confusing!