I'm not expert on OpenGraph, and it's been a while I've actually manipulated RDF other than the automatically generated og meta tags.
I'd say defining this as linked data was quite idiomatic / elegant. It's possibly mainly because OpenGraph was inspired of Dublin Core [1], which was RDF-based. They didn't reinvent everything with OpenGraph, but kept the spirit, I suppose.
In the end it's probably quite equivalent.
And in this end, why not both? Apparently we defined an RDF ontology for JSON schemas! [2]
[1] https://en.wikipedia.org/wiki/Dublin_Core
[2] https://www.w3.org/2019/wot/json-schema