Neo4j is, mostly, a very different kind of graph store. A Labeled Property Graph, and not a Semantic Knowledge Graph which is the kind of graph commonly associated with RDF.

I write “mostly” because recently neo4j has a “neosemantics” project which handles RDF. It is all pretty standards compliant RDF though, nothing custom at all.

For more information this may be a good start: https://neo4j.com/blog/rdf-triple-store-vs-labeled-property-...