My 2002 Annual Pass Guide (sleeve for the ticket) says this:
Epcot® Lunch Discount: Get 10% off of food and non-alcoholic beverages during lunch hours, Monday through Friday, for Passholder and up to three Guests at all Epcot Table Service locations. Call (407) WDW-DINE (939-3463) for priority seating. Lunch hours vary by location.
I would classify Garden Grill as an "Epcot Table Service" location and therefore assume it is included.