No; they’re not from Jordan. They’re from different places but mostly Iraq and Egypt IIRC. Even Zuheir Mohsen mentioned Jordan as a different entity from “Palestine”, to be annexed once they had conquered Israel; “Arab unity” (the pan-Arab Caliphate) was all that mattered to the PLO.
Yes the entire Paestinian movement is based on ideas from 3 generations ago. It has almost no relevance today and they need to adapt by first accepting that their primary responsibility is the peace and prosperity of their own people not the destruction and damage of others. The Palestinian movement from generations ago was so aggressive that nobody really favored it. Sure some Arab dictators and billionaires gave money and lip service from time to time but the Palestinians always ended up biting the hands that feed.
Black September 1970 the PLO based in Amman Jordan tried to kill the Jordanian king and he retaliated with 1000s dead and wounded, and the king ran the PLO out of the country. They settled in Lebanon and became drug dealers and extortionists until they set that country off into civil war and sparked an invasion by Israel and attacks from the US - the PLO destroyed that country which used to be beautiful. After Lebanon the PLO were run out to the desert in Tunisia to play guerrilla shooting at camels for a decade until some idiots in Israel and America thought it would be a good idea to give them more guns, more money and big homes in Ramallah. Yeah, it was gonna work out swell.