Flock seems to leave the data in ownership of the government. They are just providing the service of being custodians for storing and accessing that data.
You probably would get a similar response by submitting your request to Amazon web services or Google cloud or whoever has Flocks data: "sorry, we're just holding the data on behalf of Flock"
In either my example case or your stated case, you would have a very hard time convincing the host business to destroy their customers data without a court order or court case that shows their policy is invalid and they must comply.
Not a lawyer, just noting the parallel.
I do appreciate that Flock's response says that they cannot use the data they've collected for other purposes.. which further reinforces my cloud storage analogy -- the cloud vendor can't look at your data you upload to storage to e.g. build profiles on you/your business.