The WaPo writer of the posted article is engaging in some revisionist history here. Israel was born before "the Arabs and Israelis fought a war," being declared a new Jewish state by a UN resolution which partitioned the British mandate of Palestine into Israel and Transjordan. However, a group of Arab states, refusing to recognize the UN action, militarily attacked the newborn Israel, which resulted in the war referred to in the article (known as the War for Independence in Israeli history).
As for "hundreds of thousands of Palestinians fled or were expelled from their homes," those in that category were sworn enemies of the new state and could not have lived peacefully in coexistence. They should more properly be referred to as "Palestinian ARABS."
A Palestinian "diaspora"? I beg to differ. "Diaspora refers to a group of people of a particular ethnic grouping which has or had a natural homeland to which that people were once attached, now living outside that homeland for whatever reason. Since the Palestinian ARABS referred to never had a state nor a natural homeland throughout their relatively brief history, the term "diaspora" is inappropriate to their circumstances. (Historically, "Diaspora" has referred principally to Greeks, Jews, and perhaps Chinese.)
Now the million dollar question: What was the current German government possibly thinking when it paid for this Palestinian ARAB student trip to Auschwitz? There might be several possible ways to look at this from the German perspective.