Hi!
I tried playing with it a bit and noticed an oddity in the JSON format: if the predicate and object are both left unspecified, "P_" keys will sometimes refer to full statement nodes and sometimes to truthy values. An example item with not too many statements where you can witness this is Q26536085:
I think those are resolved in @context part to full URIs. The output is not just JSON, it's JSON-LD: https://en.wikipedia.org/wiki/JSON-LD
I'm not exactly sure why different ones are encoded in a different way though, I'll check into that.