I think that's the surprise he is referring to unless it is the fact some of the primers have left the stage.
Just as you now find 45 Auto in both small and large primer pocket brass, so it can occur with other cartridges. Given that primers are still in high demand, it wouldn't surprise me if it is a strategy to keep production going when one size is more scarce than the other. If you buy primers in large quantities, it may also be cheaper to buy small ones.
That said, I notice one other thing: If you look at the perimeters of the large primer pockets, there appear to be imprints of ring crimps on them that I am not spotting on the small primer pockets. So maybe the change was to address a problem with the large primers having more propensity to back out and hang things up.