You are looking at this through your own cultural lens. Take a step back and look at in the context of the broader culture and conditions in which these men live. Polygamy and much shorter lifespans for women has created a shortage of marriageable women in Afghanistan. This coupled with severe cultural taboos on pre-marital sex(in the case of Afghanistan, it's not just a taboo, it's illegal) means that for many men, especially those on the lower rungs of the economic ladder, other men are essentially the only way they can have sex.
This is not much different from any other situation where women are rare to non-existant(prison, the front lines of a war etc). In these situations men often engage in what is referred to as "trade", but of course none of them wants to label themselves homosexual because:
a) homosexuality is taboo and/or illegal where they come from and/or
b) they aren't actually gay, they are only engaging in homosexual behavior because that's all they have available to them.
It doesn't surprise me at all that men in Afghanistan are having sex with each other but not declaring themselves to be gay.....