jMyles specifically is objecting to whether the city has the moral authority to sell that exclusivity. If I sell my neighbor's lawn chair to a passerby without my neighbor's permission, the passerby doesn't have a claim on the chair even though it's my ill behavior that was the cause. (This is true regardless of whether the passerby knew who the true owner was.)
That point of the example wasn't demonstrate definitively whether the government has moral authority to sell exclusivity. (That's obviously disputable whereas the lawn-chair example is not.) The point was to show that Lyft isn't necessarily entitled to anything just because they have a signed a contract, as you suggested. Rather, you would actually have to dispute jMyles's claim on moral authority.
