On my fork I re-created the wiki for QuikGraph that I fully read and adjusted to fit evolutions of the library.
Concerning this point, the correct thing is: creates a dictionary that links edges to their parent edge, since it keeps a links between edges and not vertices.
See wiki.
On page:
https://github.com/YaccConstructor/QuickGraph/wiki/Observer-Concepts
It says:
VertexPredecessorRecorderObserver, creates a dictionary that links vertices to their parent edge,
and
EdgePredecessorRecorderObserver, create a dictionary that links vertices to their parent edge,
They are worded essentially the same. Is this intentional?
I think one of them probably should say "...that links edges to their parent vertex" but I'm not sure which just based on the class names.