Those are Frisian socks. The hearts are no hearts but leaves from the Nuphar lutea. It is a part of the Frisian flag on the socks.
Fries is a language different from Dutch. Friesland is one of the northern provinces of the Netherlands. They take pride in their language, their lakes and the "Elfstedentocht". Every winter people hope there will be an Elfstedentocht again. But most of the time, if people want to do a long distance skating tour on natural ice, they have to do the alternative route in Finland.