I always thought of nic as a drug personally, but Seems like alot of things could fall into that category. Is sugar a drug? How about chocolate? Both fit into that definition. I think even the other substances we vape are drugs .
English, unlike other languages, is one that grows as people use it. Unlike in French, there is no authoritative Academy of the English language that determines what is and what isn't.
You will find many valid definitions, validated by their own existence.
On wikipedia the definition is a bit more robust and excludes sugars:
"A drug is any substance (other than food that provides nutritional support) that, when inhaled, injected, smoked, consumed, absorbed via a patch on the skin, or dissolved under the tongue causes a temporary physiological (and often psychological) change in the body.[2][3]"