Clearly it's not Bitcoin diagram, the concept of user/account, offer service, request transaction & many more isn't exist, at least on protocol level.
Looks like it's diagram for bitcoin services or marketplace, even though real one should be more complex IMO.
You are right about that. Its not. Its as close to an UML class diagram that I found.
There's this other one that I found here, take a look if its of any use to you guys.
https://core.ac.uk/download/pdf/82440509.pdfThe only other instance that I recall is, like I said, comes from that Blockchain development group on facebook.