Yes this is true. It's a beef flavoring. My father spent the majority of his career in food-processing engineering working in a factory that made McDonald's french fries and confirmed this was the case. They're also par-cooked (pre-fried) before being flash frozen, and they don't use a batter or seasoning. Interesting tidbit, all of their competitors had their fries made in the same facility. I believe most of them even used the same type of potatoes.