This story is really unlikely on the face of it. Either they saw that shit on the x ray machine, or he was acting really weird, or they caught him via social media and used the drug dog as the pretense to stop him.

Scent trained dogs can only alert on one scent, and most of them are trained for explosives and not illegal pharmaceuticals. They can still be given a signal to alert on someone by their handler and this happens more than you would expect, since the entire point of the dog is to create a pretext.