South-West France and South-East France are all bundled as “the South” and “Occitan culture” seen from abroad, but really both areas are quite different and are two separate cultures.
Now, the term “chocolatine” is actually the original term, and it most likely comes from Austria and German (in German, “pain au chocolat” is Schokoladenbrot, if you remove “brot” (bread) what remains is very close to chocolatine).
While croissants, chocolatines and such are worldly known as French pastries nowadays, they really come from Austria. The French call them “viennoiseries” (literally “things from Vienna”). And nobody really knows why the original term stuck in the South West while it was gradually replaced by a French term in the rest of the country.