You could demand a new bike but why? The fork is made by a different company that makes the frame (bike), so there is no real reason to be concerned about the quality of the bike itself.
Possibly the guy who made the promise was not authourized to do so. YOU COULD GAIN some points by mentioning the promise but "going with the flow" and accepting the original bike with the replacement part, ( the "mark-up" on bikes is possibly the lowest in the retail industry). Shops tend to do more favors for people who "work with them" rather than making demands that may not be really necessary.

Basically you have a bad/defective PART not a bad/defective bike.

Ride Smart
Pat