Why does a 0.25 liter bottle of Kronenbourgh sometimes cost only 18 cents at Spar in France?

Hi, I'm in France on the Cote d'Azur. As you know, everything there is a bit more expensive than elsewhere. However, I went to a Spar supermarket right on the beach and bought two ice-cold 0.25 liter bottles of Kronenbourgh. I paid 18 cents each. I thought it was a mistake and kept buying more bottles there, and for the journey home tomorrow I'll buy another 10 for €1.80. So it wasn't a mistake. Of course you could say it's cheap because nobody drinks it, but that's not the case. They drink a lot and it's not that bad. A pack of six with exactly the same bottles costs around €5.
The ladies at the checkout didn't know what I was talking about. Does anyone have an explanation for this?