The behaviour is the dog salivating when the dog sees something it recognizes as food, not that the dog is able to recognize all foods. It just needs one hardwired FOOD neuron, that can be attached to a classifier that is later trained. (Idk the technical terms sorry!)
I think a mix of things are or aren’t plausible. I think the genome can’t just hardwire a FOOD neuron, because a food neuron is “about food” due to the way that the FOOD neuron interfaces with the rest of the dog’s mental machinery. I think the genome can probably hardwire an “about-to-salivate” predictor, with a known ground truth signal (did the dog actually salivate, or not?). I also think the genome can’t hardwire a circuit which fires if and only if the dog thinks it sees food.