Yeah, for years I have learned that white onion is more "spicy" than the purple one. Also, the purple one is sweeter than the white one. Has she mixed up the info? Jamie Oliver, Gordon Ramsay all said the same. Purple sweet, suitable for salad, i.e. eat raw whereas white one is best for cooking.
It's complete opposite here in US. The purple onion is sweeter, and white ones are spicier when eating it raw. Once cooked down, the white or yellow ones will turn sweet. Purple onion usually cost 1.5x or even 2x of yellow/white onions.