Did you tell them they were drinking Pepsi or ask some variant of "Is Pepsi okay?"
A pretty common interaction is:
Me: Can I have a coke?
Waiter: Is pepsi okay?
Me: That's fine
Waiter: brings a Pepsi
It seems that the above commentor doesn't have this exchange but instead silently substitutes.
Did you tell them they were drinking Pepsi or ask some variant of "Is Pepsi okay?"