Their feet are kept slightly above freezing by the very mechanism explained by the article. It's a heat exchanger, basically. Warm blood from the heart is used

Their feet are kept slightly above freezing by the very mechanism explained by the article. It's a heat exchanger, basically. Warm blood from the heart is used to keep cold blood in the extremities from freezing, and this "double loop" system is much more efficient than pushing warm blood directly into the feet where thermal losses would be much greater.