"Humanities" has become a catch-all for anything not the sciences, excluding without a doubt the hard sciences (physics, biology, chemistry), probably social sciences but not those that cross over with subjects like languages and history, e.g. linguistics is included in humanities (including in university departments) especially the emphasis is not placed on cognitive science but rather language usage, including both linguistic work and language teaching. Anthropology is often with or closely connected to the history department and so on.
That said, most colleges are still named "Arts and Sciences" though they may exclude the hard sciences in all or in part depending on what their relation to engineering is like. In any case, Wikipedia agrees that
lettres are
humanities, and the
French language article reasonably points out that there are several meanings and overlapping areas going back to the medieval trivium and quadrivium. So, the word generally corresponds to
arts libéraux, but with the marginalization of Latin and Greek, social sciences sometimes get added, though
not to the arts.
Lettres humanités (which I note are sometimes still called
classsiques) corresponds to classics (or Greats in Oxford speak), and I think that
those fit under any definition of arts or humanities (including
lettres) whether or not social sciences do as well. So, I don't want to speak above my pay grade about the French language classification, but the above-mentioned shift with classics and the influence of English, I suspect that the social sciences probably get added to
lettres more and more nowadays…
tl;dr the definition is correct as it was, without a note. Nobody is going to be severely mislead by anything that can't be easily nuanced, and while sometimes I wonder why French Wikipedia is either really long and precise or a bunch of useless stubs, in this case it's a reasonably detailed article that settles the question in an intelligible way.
