That's breakfast, lunch, and probably 5% dinner (a small minority of HQ), including cleanup costs (washing dishes, etc). You have to have some over-capacity as its a cafeteria - you can't run out of food at any time, so throw in an extra 10% - 20% food.
Then add in snacks and drinks, which come out to a few dollars a day per employee, including stocking costs, running the coffee bars, etc. That's a few drinks from the fridge, a coffee or two, a few bags of snacks a day.
And I don't know anyone working at any SV tech headquarters who don't eat the food every day. Personally I've maybe eaten not at work for breakfast and lunch...10 work days in the past year?
While the HQ gets economies of scale, smaller offices are more expensive. Y! SF catered for a long time before finally also switching over to Bon Appetit. Y! NYC provided a daily seamless stipend before they finally built out the in-house dining area.
Add in non-full time contractors as well, who generally get the eat at the cafeteria as well.
Bon Appetit is a standard, albeit higher end, food services company. They serve colleges as diverse as Cornell, Oberlin, the College of Idaho, Lewis and Clark, etc. It's the same company used by Google, Oracle, and eBay. It's hard to describe them as over-priced and overly-luxurious.