“It comes from a Palestinian port of Ascalon. Originally onions from Ascalon.”
Ascalon – or as it is known today, Ashkelon – is of course a coastal city in southern Israel. While the seaport had many different rulers throughout its history – including Canaanites, Philistines, Greeks, Romans and Crusaders – it is not and never was “Palestinian” in the sense that the majority of viewers would understand.
A more accurate explanation appears here:
Seeing as the programme will remain available on BBC iPlayer for the next eleven months, a clarification is obviously in order.