What I'm reading from that quote is that the issue wasn't renewables as such, but an issue of power generation reacting too quickly and too intensely to price fluctuations. "Renewables" only matter insofar as they're the sort of generation that, under the current regulatory regime, get to react to those pricing changes.
Stability is one of the things grid operators pay for, sometimes, but whether they pay enough and validate that they're actually getting it is another thing. One core thing the report highlights is that many of the plants on the grid didn't do what they were required (and being paid) to do.