Doesn't mean he didn't go there. Or that he did. Osama bin Laden himself did not fight the Ruskies, but he did go there, and helped provide material support.
Actually, Osama did fight at least once, in the inconclusive battle of Jadji, one of the Muj’s forward bases not far from the Pak border.
That’s how he obtained that AKR you always see in the background of all his videos—that he claimed to have won in battle from a Russian he killed.
He was probably too spaced to fight anyone, sitting there in the middle of an Afghan poppy patch worshiping all the pretty red flowers bobbing in the breeze.