He said his whole body went numb, not his mouth. Cocaine hydrochloride (powder coke) doesn't smoke well. Crack cocaine is freebase (as opposed to a salt), although what is referred to on the street as 'crack' is typically Cocaine+HCl which has been dissolved in water and reacted with baking soda (sodium bicarbonate) to yield base cocaine, water, carbon dioxide and table salt (NaCl).
Coc-H+Cl– + NaHCO3 → Coc + H2O + CO2 + NaCl
A product with a higher purity may be obtained by using ammonia and ether to yield primarily freebase cocaine. These is usually some confusion over crack vs. freebase cocaine, but crack is really just less pure freebase made with baking soda.
But anyways, if your weed was laced with crack you would sure as hell know it. Your weed would probably sizzle, taste funny, and your tongue and throat would go entirely numb. Your voice would become horse as a result. You would feel an intense rushing sensation that would subside in a matter of minutes, and then you would probably just feel kind of shitty.