Wikimath dataset description and adjacency seems erroneous

[Abusagit]

Hi! In the documentation for WikiMath dataset it's said that the graph is directed. However, while investigating graph structure, it turned out that there are no edges between nodes i and j if i >= j - adjacency matrix is upper triangular with zeros on the main diagonal.

This fact doesn't violate the property of a graph being directed, but it seems very strange, especially for such web-graph dataset, b.c. there are no loops in a graph.

Is there any mistake in the adjacency, or maybe graph should be undirected?