This isn't nothing new, at least not in the states. If someone reports what they suspect is a drunk driver and get the plate number, if police can't readily find the driver, they can go to the home and ask for a sobriety test. At least that happened to someone I knew before, arrested two hours after having gotten home. Now here in my state, the supreme court of Michigan, just ruled that cops can't search a car because they smell marijuana. That ruling came down a couple days ago. The court ruled that because marijuana is legal here that the smell of marijuana doesn't necessarily mean someone was smoking marijuana as opposed being around someone who was or in an environment where people were and that may be why they smelled like marijuana. It ended up getting a gun case dismissed after the cops searched the car after they smelled marijuana. I don't know why the guy had a gun in his car, but overall, when it comes to searching vehicles, I think it was the right call on behalf of the court as it would be way to easy for police to claim they "thought" they smelled marijuana to justify a search of a car.