http://www.gdcvault.com/play/1024656/Advanced-Graphics-Tech-... and https://www.gdcvault.com/play/1024612/FrameGraph-Extensible-...

for a more in depth view.

I would describe it as such: A scene graph specifies _what_ needs to be drawn, while a render graph specifies _how_ it should be drawn and what the dependencies of each step in drawing is. For example, a render graph is used to reduce the number of image layout transitions in a frame by looking at what layout is expected for each operation and figuring out where to put the layout transitions, instead of letting a human place the layout transitions which will inevitably lead to unnecessary transitions when the scene becomes complex enough.

I didn't think this article was bad even if it is maybe less concrete than the slides I linked.