I'd imagine a company pays to run our match day catering. Their income makes no difference to City. Could be wrong, though
The company running the catering outlets will pay a commission fee to the club, typically around 25% of net sales.
The catering operation at any stadium is complex to run, given that the non match operation is busy (Conferences,weddings parties etc) and every other week the match day operation by its very nature becomes extremely busy.
The different requirements of the two operations is stark, more staff, and complex stock and wastage issues being just two examples.
I am somewhat surprise that the club do not operate an in house catering operation, typically this type of operation will generate as a minimum 40% bottom line profit.
As an aside to those of you championing the multi beer dispensers, they are hugely expensive to install and massively unreliable, and yes I have tried to operate them in stadiums!