I don't think there is a definitive answer on exactly what the dog is indicating, simply because cannabis probably has a wide variety of odors the dog smells that we can not.
Leaf material, stems, buds, resin, all may have unique aromas that are beyond our capability to detect, but may be easy for the dog. So a concentrate may still be recognizable as a part of the whole, and would warrant an indication by the dog. The goal of the trainer is to create an association between the scent item, and the reward. However, while that scent item is just ONE scent to us, ie cannabis, the dog is more than likely creating a multitude of scent associations because they can probably smell a bunch of different scent properties cannabis has that we are not aware of.
Dogs are smart, and they're also greedy in that they will go with the "close enough" option to get the reward, if they are allowed to. So while a concentrate may not carry all of the aromas, in the dogs mind, it's probably "close enough" because it is a part of the whole it was rewarded for in the past.
I imagine it would be similar to us if we were told to "find the car". We see the car, no problem, there it is. However, if you only see a wheel, we would assume that there is a car attached to it somewhere and look harder, or we'd try to get the reward for at least finding a part of the car.
In the end, it's always easier to defeat the handler than it is the dog, as the human is the weak link in that particular team, for tracking or scent work.
