One has to wonder whether the study was skewed a bit, albeit unintentionally. What bodies were preserved enough for this analysis? Perhaps only the privileged/wealthy...so perhaps these results are not realistic for the population as a whole?
That's one of the, I guess, drawbacks of using surviving evidence. But it's not likely that all these remains were from lavish burials, or that would have been mentioned. Looks like the dating of the various remains cover a wide range, and locations vary.