I feel it would have worked better if she scanned the barcode on the bag and the register actually rang it up as dog food (instead of throwing an error at the register). It’s apparent that the infected are just reusing the dog food packaging from its original production site to package up whatever this powder mix is they’re now producing there instead.

If it was a random package with a barcode, I’d expect the register to not recognize if it wasn’t coded in the store’s database, and in that situation I’d just assume it meant the store doesn’t stock whatever the bag was supposed to be. But we saw it actually corresponded to something they stocked, which Carol then somehow managed to figure out impressively fast (not just recognizing it as a dog food bag, but the specific dog food bag among several that were stocked). Just makes less sense to me.