That does sound like Crusader propaganda, yes. And my British heritage tells me that yes, there's a statute of limitations on settlers vs. locals.

The Celts and the Britons were the OG/indigenous of the British Isles, but then the Anglo-Saxons rolled through and took the middle of the Island (modern England), and pushed the indigenous into the outskirts (Scotland/Ireland/Wales), with some mixing obviously. Then the Vikings rolled through and settled, and eventually assimilated. Then the Normans (a mix of Vikings & French) invaded and pushed the Anglo-Saxons & Vikings into the outskirts, and eventually followed them.

As a result, everyone ethnically British, from any corner of the British Isles (English/Irish/Welsh/Scottish) is really a genetic mix of Briton/Celt, Anglo-Saxon, Scandinavian, and French. Good luck sorting out the colonizers from the colonized at this point.

Regarding the Middle East, keep in mind the most common language in Biblical times was Aramaic, which over time evolved into Arabic. Both Jews and Arabs can claim to be indigenous to the Holy Land going back thousands of years, and they're both right. In fact, if you want to get pedantic, the term "Semite" technically refers to both Jews and Arabs, so it's a bit contradictory to talk about Anti-Semitism among Arabs.

As for a subgroup of Arabs called "Palestinians", that was an invention of the British Empire, but the statute of limitations probably means that Palestinian has by now become a legitimate national identity.