Hard to say what really happened there but according to some reports Ossetians had been shelling Georgian villages for days before Georgian forces moved in. Also those Russian columns appeared quite fast, surprisingly fast.
The time line is the key. The Russian military almost certainly cannot react as fast as they did, with the volume of troops and ordnance, unless they were ready to roll beforehand.
“Also those Russian columns appeared quite fast, surprisingly fast.”
Oh, no doubt the Russians had this well orchestrated to fire off during the Olympics.