The conventional advice you'll find with regard to approaching polar bears is "don't do it", usually followed by the word "ever.". They're incredibly powerful animals, more than capable of tearing a human being apart limb from limb. However even a polar bear isn't averse to accepting help when it desperately needs it; it just takes a very brave person to try. Fortunately for the mother bear and her cub in this picture, Russian soldiers aren't short on bravery.
In the Chukchi Peninsula, temperatures can drop to 25 below zero, and hard ice can form over the snow, making it impossible for polar bears to dig through it and find food. The bear and her cubs were slowly starving. The soldiers had a plentiful supply of condensed milk, and it was enough to keep them alive. Normally, a polar bear protecting its young will attack anything it perceives as a threat; it must have somehow realized these men only wanted to help.