Or rather, 'economy 101' is that anyone with enough leverage, will use monopoly powers in one area, to take control of an adjacent economy.
American Oil empires were not built on some new amazing way to get at oil, it was because some had control of the railroads, and charged their competitors a little more to transport therefore putting them out of business (through aggressive consolidation).
The FB cafeteria example is not a very good one admittedly, but an alternative could be 'they buy up all the restaurants in the area and make them exclusively available for FB staff'. Which they very well could do, and it would then seem kind of crazy, no?
Economically speaking, it would be 'above bar'. After all, 'free market', right? If neighbourhood residents want to eat in a restaurant, screw them, they can go across town!
We live in communities, not economies.
The city ordinance is stupid, but the motivation is not.
Ironically, these are 'rich people problems' ... the kinds of things that happen when little dots of wealth blow up and there is a huge economic inequality, even if most people are 'kind of well off'.