A couple of things:
From what I remember as a kid in the 1990s in the US, smoking was allowed on international flights. It was one of those grey areas that happen when traveling between countries with different laws.
I've also seen a lot of jokes about French culture being waaay more "pro smoking" than US culture.
Thus smoking beling allowed on Air France until 2000 doesn't surprise me.
Lots of Europe especially France is packed with smokers. One of those things you take for granted living in the US and once you travel abroad you realize how much of the world still burns tobacco and it’s everywhere.