[WayneS]

In addition, past population sizes were estimated, and showed that a continuous swathe of populations from the Balkans to the British Isles underwent an explosion in male population size between 2000 and 4000 years ago.

So then, this is all based on some guy's GUESS as to what the populations of parts of Europe were over a 2,000 year span, more than 2,000 years ago.

[Crystal Palace East]

Beats Obama’s guess of what it means to be an American.

[OK Sun]

If you're interested in the procedures the used, you can read the paper to see how accurate you think they were:

Samples and approach. To address the lack of a systematic population-based NGS study of European MSY diversity, we assembled a collection of 20 randomly chosen male DNA samples from each of 17 populations from Europe and the Middle East (Supplementary Table 1).