Nope. It's clearly the popularity in high school. It's amazing what sort of effects your early years, and especially those people around you in your middle years can have. What happens is, basically, everyone in your high school class calls up your future employer and says either "raise his wage" or "lower his wage". The future employer uses their consensus to decide your salary. It's really fascinating.
In other news, ice cream truck drivers now on trial as accessories to murder during summer time.
[edit: So it doesn't come off as otherwise, I'm not snarking you. From a preliminary glance, it certainly looks like they might be doing that whole "correlation == causation" bug that can happen very frequently. Your analysis seems reasonable to me]
If you don't want to read the whole paper, the interesting sections are, Table 2, sections 3.2 and 3.2 (including Table 3), and, of course, the intro and conclusion.
Frankly, I'm surprised the wage premium for popularity is so low. The wage premium for managers (and execs) is high, and folks who have good people skills are much more likely to become managers. So, why isn't the wage premium higher?
I feel like this is much more about the results of high school popularity (confidence, self-assuredness, dare I say getting laid?) than the actual implementation of popularity itself