When you look at the interdigital scent, it is white and waxy. Doesn't seem like it's scent could instantly change or could be produced rapidly (upon a wound). The only thing that would make sense to me is the amount of scent being dropped. When a deer stomps, it is depositing the scent for other deer to smell and be alarmed. The scent in small amounts is natural, but when there is too much, other deer are warned. Often deer that are shot have trouble running and will run heavy footed so to speak. Maybe an increase in the scent deposited along with microscopic blood droplets gives the dog an instinctive clue that the deer is wounded, following a scent trail undetectable to humans.

Just my theory...

I used to use a stalking stick to sound like a 4 legged animal walking and not a human and would put interdigital scent in a slot at the bottom end of the stick. I've had deer, dogs, and coyotes come up trying to find me. The key was to deposit a trace amount and not too much.