This is a nice sandbox walkthrough of the author's objective which was to test MSFT claims in the paper -- but with all due respect the buzz of graphs is because they add whole third layer in a combined approach like Reciprocal Rank Fusion (RRF). You do a BM25 search then you do a vector based nearest neighbors search and now you can add a KG search then all combined with local and global reranking etc the expectation is this produces a better final outcome. These findings aside, it still makes sense that adding KG to a hybrid search pipeline is going to be useful.