From the article Combien de mots existe-t-il dans la langue française ?
selon les Immortels, le jargon des chimistes compterait plus de 100.000 mots rien que pour les matières colorantes.
Google Translate:
according to the Immortals*, the jargon of chemists counts more than 100,000 words just for coloring materials.
Why are there over 100,000+ words for coloring materials in French?
*l'Académie française
100k is a theoretical gross estimation of the number of distinct coloring materials but no dictionary lists them.
In chemistry, molecules are described by their formulas and from these formulas, a name can be coined by following strict agglutination rules. There is however no much point to list all the almost infinite possible combinations in a dictionary.
This is what the 20 minutes article wrote:
selon les Immortels, le jargon des chimistes compterait plus de 100.000 mots rien que pour les matières colorantes.
Note the conditional meaning it's an unconfirmed hypothesis. The original quote found by @None is slightly different as it talks about the number of materials, not their names but the idea is the same:
le Dictionnaire de la chimie de Duval, loin d’être exhaustif puisqu’on distingue plus de 100 000 matières colorantes, comptait déjà 26 400 entrées en 1935, mais plus de 70 000 en 1977 !
Loin d'être exhaustif means that the dictionary is far to be complete so the idea is that there are (very roughly) 100k coloring materials but only a tiny fraction of them have names listed in the Duval dictionary, especially assuming that most of the dictionary entries do not relate to coloring materials.
The point made by 20 minutes and by the Immortels is that there is no sensible limit to the number of words of a language if we decide to include words that have at best a very specific use but might also have none.
This reasoning can apply to a synthetic languages like German. A few words like Aufsichtsratsmitgliederversammlung or Rindfleischetikettierungsüberwachungsaufgabenübertragungsgesetz might be listed in German dictionaries but all possible words can't.
I can answer that question from the chemical side.
First, the number of possible molecules is infinite. If you restrict the list to commercially available molecules, there are various estimates of that number, the latest I found being:
scientists have created a global inventory that lists more than 350,000 chemicals and mixtures of chemicals registered for commercial production and use, up to three times as many as is commonly estimated (Environ. Sci. Technol. 2020, DOI: 10.1021/acs.est.9b06379).
I note that the previous number “commonly estimated” must therefore be close to the 100,000 estimate given in your source.
Secondly, all molecules have a name, thanks to IUPAC rules of nomenclature. Often, they even have several possible names — but only one preferred name.
Finally, one part of the quote strikes me as odd: why restrict this list to “matières colorantes” (a somewhat dated way to say “colorants”, or dyes in English)? This is a particularly specific choice, why chose this category of molecules, and not “100 000 molécules” or something else?
As None's deleted answer mentioned based on the following dictionnaire-academie.fr, the Dictionnaire de la chimie de Duval may contain many entries for coloring materials:
Si l’on parle de la langue française (ou anglaise), de quoi s’agit-il ? Prend-on en considération tous les domaines, toutes les époques, tous les niveaux de langue ? Il est impossible de fournir un dénombrement de l’ensemble des formes qu’offre une langue : certaines (comme dans le cas de tous les verbes que l’on peut composer avec le préfixe re‑) n’ont qu’une existence virtuelle ; chaque jour, d’autres se créent ou disparaissent de l’usage. Le vocabulaire spécialisé des sciences est en constant développement : le Dictionnaire de la chimie de Duval, loin d’être exhaustif puisqu’on distingue plus de 100 000 matières colorantes, comptait déjà 26 400 entrées en 1935, mais plus de 70 000 en 1977 !
Note that one entry may comprise more than one word. Therefore, 20minutes' sentence "selon les Immortels, le jargon des chimistes compterait plus de 100.000 mots rien que pour les matières colorantes." is incorrect: 20minutes confused mots with entrées and quotes from les Immortels doesn't say how many entries there are for coloring materials.
Here is how the Dictionnaire de la chimie de Duval looks like, from issuu.com:
