If you're in current, the current can hit your buddy and push him toward you; you'd think you'd get pushed away at the same rate, but if you're in the shelter of his "current shadow", that may not happen.

But the most likely explanation, if you're facing one another, is that you're both finning to remain stable, and even a tiny amount of that will push you toward one another.

Ascents are one of the places where back-kicking shows its value