Ah, no they didn't.
1) People misread the request for quotes. They multiplied the max number of rounds by the delivery quantity. So in a given caliber, the gov asked for a quote for say 100,000 rounds with a delivery quantity of 1,000 rounds. That means the successfull company would supply UP TO 100,000 rounds, in quantities of 1,000 rounds (1,000 or 2,000 or 3,000 rounds, etc per order). So some brilliant people multiplied the 100,000 by the 1,000 and came with with quantities of 100,000,000 million rounds.
2) The DHS order that is commonly referenced was for actually about the same number of rounds as the year before, but for the first time, DHS was putting out a comprehensive contract, instead of each group ordering separately. So under this contract, was all the ammunition normally ordered by CBP, INS, Secret Service, etc.
3) It was a requirements contract, they did not order all that ammuntion, they got a contract that allowed them order as they need, UP TO the maximum numbers of rounds in the contract.
4) The contract was not a single year contract. It was for the prime year plus option years. These types of contracts allow a company to plan ahead, that they can figure on business for several years. Which gives a lower price to the government.