I am not sure who wrote it, or where to even find it again, but I have read exactly what virmundi is referring to. It is possible he is confusing authors.

The long and the short of the document was that a REST client must be able to navigate the entire API when given just a single endpoint URL, much like you can navigate an entire website just by entering the homepage URL into your browser, but without the dependance on HTML.

The leap the document made, and what virmundi seems to be referring to, is that a REST client that speaks, say, JSON is not enough to traverse any random service, as everyone will provide a completely different JSON representation of their data. When you start hardcoding site-specific keys in which to find the action descriptions, you lose all of the flexibility the author claimed REST would provide in the first place.