I know a bunch of women at ivy league universities that can't find a partner and would say it is definitely mostly (1). The article seems to put its main focus on men feeling their manlihood threatened if the woman has a more accomplished career, but I'd point out that these women perceive a significant social pressure that they're able to find a man that is more accomplished than them.

In fact I'm in that kind of position myself, and it doesn't feel threatening to me at all.