French Pineau Charantaise in WWII

I am reading memoirs of Hans Werner Woltersdorf called “Gods of war”. This German soldier was stationed in Montboyer, France in WWII. He says “it was forbidden to make Pineau during the war”. Why, for what reason? This question may seem off the general topic but, firstly, there are French members of the forum who may know, secondly, book’s author says on the next page “The food train was fifty cars long…all of it amminition for the field kitchen”.

Perhaps because of 'loose women", I remember visiting the Liege Museum in 1966 ad coming out one exit seeing stenciled “OFF LIMITS” signs in English, on several walls. The curator told me it was a left over from WW II.

Pineau is a kind of liquor like Xeres, Porto, Muscat, aso
to make it first you need to convert the grapes to vine and after you have to add some Cognac.
Cognac being alcool, I think it is because of that it was forbidden