I think this is an essential part of the analysis. The author makes a point of matching pairs of players who have played each other across multiple time control

I think this is an essential part of the analysis. The author makes a point of matching pairs of players who have played each other across multiple time controls so that he is comparing the same population of people across multiple time controls. Reason this is important is because the Blitz playing population is not the same as the Rapid or Standard playing population (they are literally a different mix of people and sizes of population), so you can't compare these populations directly against each other.