Not exactly what _I_ was thinking of, but that's because I was headed down the smoked/jerk path. ;-) Obviously a real botulism risk. Other sources indicate that stuff preserved this way (whether in a crust, crockery or a tin) should be kept in a cool, dry, place. According to a book I found on Questia, other near-contemporary sources to the William Salmon book indicate that meat pies had a tendency to go off around midsummer, so that whole keeps for a year thing was optimistic.
Context is everything.
Here's the most annoying bit:
p 46 Clarkson: "Keeping a meat pie for a whole year without refrigeration is a terrifying thought today, but it was such a common practice that we have to assume that most of the time consumers survived the experience."
Actually, we don't. First of all, not all sources claim a year -- some very much the contrary. Second, "without refrigeration" is misleading. People were pretty emphatic about keeping this stuff in a cool, dry place. Third, most of these things wouldn't have been kept around for a year; they would have been consumed much earlier. Finally, there were a variety of other practices prevalent for decades during the European middle ages that killed more than half the participants. Weaning at birth, as practiced in Iceland and parts of Austria, springs to mind.