You get that when you hit fuel cut, but fuel cut could never be mistaken for a backfire...at least I _hope_ it couldn't be. Are you really backfiring, or are you hitting a brick wall while at full boost? Successive fuel cuts causes that code and is not good for your car. Adding an FMIC and being in cold weather would be a recipe for fuel cut, especially if you're not tuned or are tuned by someone who doesn't remove fuel cut.
If your boost was set to 19-20 in normal weather, then you probably are running more than that now. However, it's not really about how much boost you run, but rather how much air you flow across the MAF. In the winter, even at the same boost level, the air is more dense and thus more likely to reach the built-in air flow limit for the ECU.