Not a perfect match, but it indeed points at something.
Most level-headed people know the deal with soy, but other plants also contain phytoestrogen. Things like rice, beans, carrots, alfa-alfa seeds, sesame seeds, oats, wheat, coffee - all disrupt the male endocrine system. Just picture what vegan's breakfast, snack, supper, snack, dinner, snack, and snack contain.
I also suspect that a weak nutrition profile, in general, is cause for low sperm count in men, just as it causes premature menopause in women. It's almost like the body starts ignoring reproduction if famine is on the horizon, and veganism simulates just that.
I was vegan for two years, and near the end, I was unable to have a sexual climax. Not to mention a host of other little issues that were either new or worsened during that period.