At this point, we really don't talk about using Blueprints level Graph API for doing things. Folks operate at a Gremlin level. There's some references to the Graph API in the book that should probably be removed, like: "4.5.1. Adding an airport (vertex) and a route (edge)" which adds a detracting statement of:

While using the graph object in this way works, it is strongly recommended that the traversal source object g be used instead and that vertices and edges be added using a traversal.

Not sure if there are other references to it offhand, but I think it's worth a good going over to clean that up.