Before the war, there was a certain amount of anti-British feeling among some sections of the Dutch people. This was a hangover from the Boer war, and was connected with the British practice of putting people in concentration camps. Not surprisingly, during WW2 Britain was seen as a possible saviour of the Dutch and feelings changed. Air drops of weapons, etc. to the Dutch resistance, plus the provision of a place of refuge for the Dutch government in exile, a safe haven for Prince Bernhard, and (I think) for Queen Wilhelmina, all served to raise the profile of Britain in the wartime Netherlands. Of course, the sight of British troops on Dutch soil was the ultimate blessing for the Dutch people. The Dutch are well known for welcoming (some) foreigners, so a comment on your friends' case, in Amsterdam, is not really possible here. Do your friends speak Dutch? That in itself is not a major problem in the big cities, as many Dutch people speak English, but it is seen as a compliment if a foreigner makes an effort to learn something of the language.