It doesn't seem plausible over such a distance. And the dog sat upright immediately as my friend exited the building - no time for a scent to drift over, even in a high wind (it was a calm day).
Dogs have really good noses and the difference of air pressure between the store and outside could make a scent move far faster than you'd think. I'd see scent as far more plausible than psychic powers at least.
I mentioned this in another comment, but one explanation could be that the person in the car started to smell different due to seeing his friend. Pheromones from subtle excitement.
Right! I can't refute that. I wouldn't have thought of it, and that's why it's important to have other eyes on descriptions of these phenomena.
Furthermore, this is something we can measure, and hypothesize, and predict - Science.
This discussion got me thinking about all the pheromones we emit, but can't really sense anymore. I wonder what sort of information are we constantly spreading that essentially no one is picking up. Or maybe we are, but only on a very subconscious level.
Not plausible for a human but maybe plausible for a dog?