From the article...
"Studies based on the apparently flawed method have suggested Earth's biodiversity remained relatively stable - close to maximum carrying capacity - and hinted many signs of species becoming rapidly extinct are merely reflections on the poor quality of the fossil record at that time."
Estimates of biodiversity and extinct rates has been based on a fudge factor that is now being questioned for its validity. This means that the results of the analysis in many papers is in question, based on use a fualty factor for normalizing the results.
This challenge based on simulation data, so it is not hard empirical evidence.
The debate on how to tally these numbers continues... http://phys.org/news/2016-10-flawed-analysis-years-evolutionary.html