I just sent a customer comment to Subway asking for clarification. I'll post the reply when it comes in. I'm curious as well because mine was filled as well, and I want some ammo if someone tries to rip me off in the future.

By the way, take a look at the Subway website. The new salads are right there on the front page, and are brimming over spinach. According to the nutritional data, the spinach salad is the smallest (at 260 gram servings) but it only doesn't get the normal toppings that the other salads do which would account for the lost mass.