A neighbor who became a Sheriff described the smell of meth to me once as smelling like a hot/burned cd. Not sure if he meant burning as in fire, or the smell of a freshly burned as in imprinted with data, but that’s a distinctive enough hot plasticky smell with chemical overtones. From what I remember of how pot smells it’s absolutely nothing alike...not an aficionado of the stuff but I remember from others having it around that it smelled, well, plant-y.
Either way...not buying this.
I postulate they smelled pot and upgraded their story after they filled Grandpa full of holes.