Security concerns? The same article states "the app had to be downloaded by bypassing a phone’s security settings" (emphasis mine)

No kidding - the instructions for the app itself came with a "secret pin code" printed out on paper for the volunteers to use to install it. Why not just give them a "secret pin code" to call in with to verify who they are, its just as secure.

The story when it fully comes out will be quite interesting. The assumptions that we all are making are almost certainly to turn out wrong in some way - I'm looking forward to trying to compare the ways in which I was wrong on my thinking today given the relatively sparse reporting thus far.