Actually, while it is true polar bears are good swimmers,
young polar bears are not as resilient when it comes to swimming long distances, which they are having to do more and more as the ice floes break up due to global warming. Many more of them are dying because of this than used to be the case. Wouldn't surprise me if what the picture showed was one suffering from exhaustion after having been on a long trek with its mum for food and trying to recover on whatever 'land' was available.
Enjoy your 4x4.
Chock