Top heavy rocks like that would be in a state of unstable equilibrium - they might balance for a second or two but if you even breathed near them they'd topple.
There is a clue on his website. The temperature was minus 5 C. The rocks look wet. I suspect there is a thin layer of ice between the rocks which overcomes the tendency to topple as long as they are finely balanced and held there while the ice forms. He does say if it's windy, they come down.
Replay available now: A handful of emerging network technologies are competing to be the preferred wide-area connection for the Internet of Things. All claim lower costs and power use than cellular but none have wide deployment yet. Listen in as proponents of leading contenders make their case to be the metro or national IoT network of the future. Rick Merritt, EE Times Silicon Valley Bureau Chief, moderators this discussion. Join in and ask his guests questions.