Wrong.
There was no visible sign of drug use in the car in this case. If the cops saw him smoking a joint in the car, they would have probable cause without the dog, and they would have probable cause to use a dog to find any hidden drugs in the car.
And you completely dodged commentary about the other case where SCOTUS ruled differently in a similar situation.
1 - To a drug dog, the smell would be as obvious as sight is to a human.
2 - Thermal scans of houses target people. This was a cop with a drug dog who happened to stop a car.
In Kyllo v. United States, the authorities used thermal imagery to specifically target the house owned by someone they already suspected. And since the house wasn’t going to move away, they had time to get a warrant.
Also:
“The majority opinion argued that a person has an expected privacy in his or her home and therefore, the government cannot conduct unreasonable searches, even with technology that does not enter the home.”
You don’t have a reasonable expectation of privacy while driving a car on a public road.
Held:Where, as here, the Government uses a device that is not in general
public use, to explore details of a private home that would previously
have been unknowable without physical intrusion, the surveillance
is a Fourth Amendment “search,” and is presumptively unreasonable
without a warrant.
http://supreme.justia.com/cases/federal/us/533/27/case.html
“In 1991 Agent William Elliott of the United States Department of the Interior came to suspect that marijuana was being grown in the home belonging to petitioner Danny Kyllo, part of a triplex on Rhododendron Drive in Florence, Oregon. Indoor marijuana growth typically requires high-intensity lamps. In order to determine whether an amount of heat was emanating from petitioner’s home consistent with the use of such lamps, at 3:20 a.m. on January 16, 1992, Agent Elliott and Dan Haas used an Agema Thermovision 210 thermal imager to scan the triplex.”