The context of this question is the Ars Subtilior music from the end of the 14th century in France. Several songs from that repertory include references to fumeurs & fumeux which we would translate today as "smokers" & "smoking." However, at the time, the connotation of these words was different and the answer to the question "Did the fumeurs intentionally inhale smoke?" is a difficult one.
There are a couple of ways to deal with the question. First, it must be noted that "smoking" as it is currently understood did not exist at the time. There is no record of any kind of smoking as a social activity in Europe until shortly after Columbus. When it was introduced, it caused quite a stir. Long-time Old World drugs such as hashish & opium were originally eaten. So one might conclude that the fumeurs could not have been smoking (as we understand it).
However, one has to ask, even if the vast majority of people in France at the time had never heard of "smoking" (i.e. the intentional inhalation of smoke), what about people called fumeurs? That is a natural question, because historians cannot say with certainly what every living person did or did not do, especially in his private moments. Indeed, "smoking" presents no technological barriers, as all it requires is something to burn and a way to light it on fire. The ubiquitousness of fire as a source of heat and frequent lack of ventilation almost seem to make this "discovery" inevitable. In fact, archaeologists have discovered traces of burnt drugs in pipe-like objects in the Old World.
So we are left with not much of a case either way, and must look at the question in a different light. Just what was meant by fumeux? To begin to answer that question, it must be noted that this period saw a sort of "lobbying" for a fifth humor to be added to the traditional Greek set of four (blood, phlegm, choler, melancholy). And that humor was "smoke." So perhaps fumeux should be understood entirely metaphorically. Well, perhaps not. After all, humors were supposed to be balanced in the body and might need either to be increased or decreased (i.e. leeches), and let us not forget that the original humors were real substances (the latter two being forms of bile). So it is possible that the use of smoke as a humor could have either inspired or been inspired by "smoking" of some sort.
It seems that this "humor" definition was more pervasive than previously imagined, and indeed that fumeux would be better translated as "fuming" where an excess of that humor caused it to leave the body in a particular sort of way, emotionally speaking. (Note that this should not be read as anger or wrath.) The fumeur songs can be understood in this way, although there do seem to be some rather pointed double-meanings left dangling. The exotic harmonies of these songs have also been suggestive of drug use to many listeners.
Perhaps more significantly, the texts of these songs are all linked to the poet Eustache Deschamps (1346-1406) who left enough writing to fill 11 modern volumes. Deschamps is also known to have written the text set by Andrieu on the death of Machaut in 1377, for instance. Deschamps' use of the terms fumeur & fumeux is apparently in a satirical vein, and suggests the answer to what the "double meanings" in the songs might have been. Indeed, this piece of the puzzle allows us to understand the songs without positing that there was "smoking" going on at all.
The current consensus among musicologists is that there was no physical smoking, although proving such a conclusion will likely remain difficult. At present, the argument is essentially an invocation of Occam's Razor.