There isn't actually any chemical reaction taking place. The meth is heated, first it melts, then it vaporizes, but in the process it doesn't mix with other chemicals. It just merely changes state. Smoke, as I understand it is a chemical reaction. it combines with oxygen and releases smoke and ash, the end product is 2 entirely different chemicals.
Not that it really matters, people are probably going to go on calling it smoke anyway, and not that I condone illicit drug use in any way, but was just curious, technically is it smoke or vapor that is inhaled?