I don't think that's the assumption at all. My personal experience is, unless you happen to be located where one of the "best" developers is, they simply won't move. So you have your choice of them working remotely, being lucky, or not hiring them.
I took this to mean (a) be relative to the office specifically, not the industry generally, and (b) that those very best will get sick of the required face time, quit, and get a better job (the insinuation being that that better job will likely be majority or entirely telecommuting. I may have misunderstood the intent as I commented pretty much immediately after reading it.
I just generalized it to my experience, which is less about introvert/extravert and more about "bad conditions force good people out/prevent good people from being hired"
I, too, read "group" as "extroverted engineers," and I don't really see alternative readings.