What he saw shocked him for life and as you brought up the subject he was vehemently pro Palestinian for the rest of his life
How interesting that they have such different experiences on this
So he saw a five nation Arab army invade a fledging new state of refugees, many of whom had just survived the Holocaust, and thought "these are my people". Those same Arabs who were also allies of the Nazis during WWII?! So he took the side of the aggressors. Riiiight. Either this never happened, or someone had some serious issues.
Just a quick history lesson then. A partition plan won UN approval to give the Arabs half the land, and to give Jews half the land. The Arabs did not accept the plan - they didn't want half of a loaf, the wanted ALL of it - and so they declared war on the Jews with the intention of killing them all and destroying the fledgling Jewish state. Essentially it was their intention to "strangle the baby in the crib", so to speak. The war took place in two phases, firstly a civil war between Jews and Arabs in Israel. As civil wars are, it was fierce and cruel with many deaths. Then, in the second phase an Arab army made up of Egypt, Transjordan (now Jordan), Syria, Lebanon, and Iraq invaded.
In that war, yes, Israel did take more land than they received in the partition plan, but they were fighting for survival. It was a defensive war to begin with, then it became offensive for to shore up their long term security (there’s nothing unusual about that, that’s how war goes usually). Jordan took the West Bank, Egypt the Gaza Strip. Palestine (a territory only in name, NOT a country) ceased to exist.
The fellow Arab nations could have set up a proto-Palestinian state in those areas, built, invested in infrastructure. But no, they preferred to do nothing for the Palestinians in the refugee camps, who sadly paid the price of the Arab failures.