The golfing ones are a bit more extroverted and charismatic than the non-golfers; they "look like CEOs". They are more likely than the non-golfing ones to have attended a top-tier MBA program. Their average height is significantly greater than the non-golfers. And so on; you see where I'm going.
Certainly there are plenty of introverted, socially challenged golfers out there. But within any population whether CEOs or lawyers or cops or musicians or whatever else, the subset of people who golf is going to be, on average, more extroverted than the subset of people who don't.
I think this somewhat ties in to Taleb's argument that you should trust surgeons who don't look like surgeons, since their achievement of professional success despite their tendency to create a negative first impression is a robust heuristic of professional competence[0].
The population of non-golfers, averaged out as a population, were held to subtly higher standards that required better performance out of them. This means that non-golfers, as a population, tend to be more challenged at work over the course of their careers, and that it was less likely that individuals could "fail up" -- the Peter Principle extends further for extroverts.
Anyway that's my theory.
0: https://medium.com/incerto/surgeons-should-notlook-like-surg...