It wasn't just Super Tuesday in the US yesterday, it was all over the world. These people are in Amsterdam, at De Balie, voting in the Democratic Primaries. Their organisation, Democrats Abroad gets to send 22 delegates to the conference in Denver at the end of August (the whole organisation, not just Democrats Abroad NL, of course).
Also check out this report from CNN's Robin Oakley about the voting by Democrats, abroad. (But ignore the part where he says India instead of Indonesia.)