I'm gonna try and simplify what Persuader is trying to say:
If you travel to Paraguay, Mexico, Colombia, Brazil and ask anyone you see on the streets:
"Are you an american?"
They'll say:
"Of course I am an american!!! That's the continent I was born and live in."
They know they are americans but that's not their primary identity. They don't spend their lives thinking about themselves as americans but as Paraguayans, Colombians...
Persuader is saying that something very similar would happen if you could go back in time and spend a week in Palestine in 1820. If you stopped 10 passers-by going about their business and asked them:
"Are you a Palestinian?"
They'd reply (after thinking for a moment and somewhat surprised):
"Yes, that's how the Romans used to call this part of the Levant and even today every now and then, someone refers to this part of the Ottoman Empire as Palestine. So you can call me a Palestinian if you want to." (smiling, amused by the thought of thinking about himself as a Palestinian).
They knew that one of the names of the region was Palestine but none of their main self-identities was Palestinian.
The people you talked to in 1820 in Jerusalem, Jaffa, etc... thought about themselves as:
1 Arab, Jew
2 Muslim, Christian, Jew
3 Ottoman
4 His/her arab clan
Palestinian wasn't even their fourth identity.
So Persuader is absolutely correct when he says there was no Palestinian people before the Zionist movement started colonizing their homeland.
Just like there was no South African black people in 1500, 1600, 1700 before the Dutch started colonizing their land but only Zulus, Xhosas, Sotho and many other Bantu peoples.
Just like there was no Indian in the 13 colonies who identified himself as an American before 1600 when the English arrived.