I honestly love startups which do more business/process innovation than cool technical stuff with no actual utility. There exist hungry workers and slack kitchen capacity at restaurants in every major metropolitan area, every single day. There exist catering companies but they all have to maintain their own kitchens for sourcing.
Connecting the kitchens and the workers leads to eliminating expensive waste. Yay. Predictable incremental revenue streams for restaurants on weekdays are amazing from their perspective. After having customers and data, a couple iterations down the line I think they can probably offer something as compelling to the food customer -- e.g., fixed pricing, which could make this very competitive with business catering. That is almost certainly a 9 figure a year business in NYC alone.
[Edit: Someday, I want to hear the story of the early days of this company. I'm having visions of the MVP involving 0 lines of code, one cell phone, one inbox, and a whole lot of hustling. "Hiya skeptical restaurant manager, I'm calling to place $1,800 worth of food orders for next Thursday. Also, I want to do it twice a week for the next six months. Do I have your attention? Great, here's what we're going to do..." Repeat a couple of times while becoming the Official Food Logistics guy for the YC mafia, and suddenly you have side of the two-sided market bootstrapped from zero to "You are their favorite person ever", plus you've got a very good understanding of what sucks about ordering food for a large number of people. Then you start coding.]
I won't speak for them... but I can guarantee there are countless stories like this... along with "OMG WHY ISN'T MY FOOD HERE WHEN I ORDERED IT!!!!" and "THIS FOOD IS SO AWFUL ZOMG ZEROCATER I'M COMING FOR YOUR HEAD!!!"