The word "concept" here is doing extreme amounts of heavy lifting here.

If I had to bring the point home I'd say that the author himself committed the very mistake he is warning against in that very sentence.

Frameworks define conventions and non-language features (language feature=data structures, callable functions, etc) that cannot be expected to be understood by simply reading the existing code and therefore need to be learned explicitly by reading the documentation of the framework. Frameworks are allowed to bend rules and expectations, because you're supposed to learn and be aware of them ahead of time.

This directly applies to the irresponsible use of the word "concept". The meaning of what he was trying to convey cannot be understood based on simply reading the sentence.