This is hardly a shock:
In an exclusive interview, Gen John Nicholson said he'd seen "destabilising activity by the Russians."
He said Russian weapons were smuggled across the Tajik border to the Taliban, but could not say in what quantity. Russia has denied such US allegations in the past, citing a lack of evidence. [emphasis added]
Innocent people say they didn't do something they are accused of doing.
Guilty people tell you there is no evidence to clearly demonstrate they are guilty.
While Russians are naturally really good at lying, I suspect that the Russians let officials at the Afghanistan Desk not trained in the art of lying speak about this issue.
Perhaps their best liars are at the Ukraine Desk where they demonstrate that Russia is fully capable of invading a country and simply denying they are doing it.