I can 100% assure you that it has pig fat, I don't have any written evidence to support my claim but I know people that work in the manufacturing / head office and well they have told me... And really your suprised that McDonalds would lie, they would do anything for profit and considering that the quantity of veg'ns has risen exponentially over the last decade this is even more true ever then before; they will attempt to lie and say their products are animal friendly but fact of the matter is that it is cheaper for them to lie then it is to actually integrate animal friendly options into their menus.
I'm not trying to defend them, but surely lying about the ingredients would not be a good business decision?
From the website: SUNDAE MIX: Milk, Milk Solids, Sugar, Cream, Glucose (from Wheat or Maize, contains preservative Sulphur Dioxide), Emulsifiers (433, 471), Vegetable Gums (407, 407a, 412, 466), Flavour.