Adding sugar to wine is considered a great offense, and is not only illegal in France, but a disagrace. Still, some winemaker wake up in the middle of the night to do it in secret because it's hard to get a sweet taste or more alcohol naturally. Therefor, the anti-freeze workaround is not surprising.
It was a simplification on my part. If you want to be precise, then chaptalisation (the process of regulating alcohol quantity using sugar) is illegal in south of France vineyards, forbidden everywhwere when mixed with acidification processes, and allowed but under very strict conditions otherwise in "septentrionales" vineyards (which I have no idea how to translate in English).
