Terma claims that their surface movement radar is installed in Vnukovo:
http://www.terma.com/media/195921/sm..._may2012__.pdf
It would seem that either the ATC was asleep at the wheel (figuratively speaking) or the SMR was out of order. The snow plow guy could have driven onto the wrong runway by accident, and failsafe systems meant to prevent this kind of collision somehow malfunctioned.