If you read it something somewhere, it doesn't mean that it's true. Requirements gathering was always an important topic in the PMBOK, and its importance is increasing with every version of the PMBOK.
I'm sure that the above authors are pro-agile, and I'm saying this without reading their article (as it'll be most likely full of similar intentional errors).
Another comment I would like to make is that Waterfall (PMBOK) is accused of being a linear methodology. For example, you can't go back to planning once you are executing the project. This is false, Waterfall is iterative through change requests.