Yogurt can be a base rather than a topping
The idea
Yogurt can form the body of a dip, with vegetables and seasonings worked into it. That gives it a different role from a spoonful added on top of a finished dish. The final texture and ingredients depend on the particular preparation, so appearances alone are not a reliable guide.
A practical next step
Ask about dairy in sauces and dips as well as in obviously cheesy dishes when discussing dietary restrictions.