Hello All dear peoples of the DreamWorld's Forum
I am french, and I never heard about a "special cocktail" about July 14th ( national commemoration for greeting the Bastille's tour ( a prison at this time, where Marquis of Sade was jailed ) been down for revolutionaries , so callled the fall of noble rules over the french folks ( think that just after there was a périod called "the terror" and the rise of Napoleon, you know now how special French peoples may be

)
Anyway, at July 14th the tradition is about dancing and fireworks ( fireworks for memories of gun shoot and and cannon strikes, Dancing about the peoples pleasure to be liberated )
The cocktail you discribe Mister TightFit74 reminde me more a "Champagne soup" ( the name ). Not special for the commemoration, even in the place you were, this is maybe the occasion to drink this one particularly.
Ardeche is more know for red wine ( strong one ) but ... that's not the only place were red wine is made in France ...
Sangria is spanish and made for red spanish wine and fruits like oranges, citrus , apples ... I drunk a lot in Barcelona were it almost replace the water to drink

Please accept my best Humbly Regards.