As the author suggests, instead of just letting it fester, I caught him at an opportune moment and asked him if I had done anything to upset him (I suspected maybe a not-tactful-enough code review may have been the culprit.) He just denied that anything was wrong, other than that he wasn't sure how to relate to me because our circumstances are so different (I'm quite a bit older than him and have a family, although it hadn't been a problem before.)
Unfortunately this interaction just made our relationship even more awkward, and it never recovered. He ended up leaving the company about six months later.
In summation, simply getting things out in the open is not necessarily the cure-all the author suggests it is.