Most of the cost was labor, according to the picture in the article. I don't know which dining hall or cafe the "canteen" they're referring to is, but much of the food sold on Harvard's campus is produced by unionized dining hall staff with decent pay, hours, and benefits, which affects the costs.

Personally I could see that information back firing, some places are very stingy with ingredients like chicken, and I'd feel doubly cheated if they did that after admitting it's only 5% of their total cost!

This was in a cafeteria.

At Harvard