I'm not sure how this stands up if you control for the the obvious selection bias. After all most people aren't going to switch jobs unless there is a substantial pay hike.

Much of the data could be because people who are significantly underpaid can and do switch jobs and get a big salary bump to market rate. But once someone is at market rate, it is difficult to find a job that pays super market rates, so they stay put.

The authors don't provide any longitudinal data to show that serial job hoppers get paid more over the long run. They provide anecdotal hearsay, and a questionable extrapolation from statistical data.