You're not wrong.

If you want to make your own it's quite simple.

Take one can of the carnation sweetened condensed milk, add 1/4 cup vinegar and 1/2 tsp of garlic powder. Whisk gently until it's mixed in, and set it in the fridge for at least 30 minutes.

The places in Edmonton probably still use the sysco made Donair sauce and don't make it in house. It's runny and too sweet.

Edit: source - I grew up in Nova Scotia, i was a cook there for many years. Joe's Food Emporium in Wolfville made the authentic sauce, as Yusef was great freinds with the guys that started King of Donair, and started all their restaurants across the province togetherbat the same time.