I saw NFL Live, I believe it was, a couple of days ago and they were breaking down the Flores defense, pre and post snap analysis. Alex Smith was calling the pre-snap read. He was wrong on all three that he called. Post snap, the safeties were low in the flat, normally where the corners are, and the corners had dropped back and where playing deep where the safeties would normally be.
One of analyst gave the best description that I've heard so far and that is the Flores defense removes the opposing team's offensive coordinator from the equation and puts it all on the QB, who has to read it on the fly and none of the defenders are where the QB expected them to be.