I wonder if it was vinegar and he didn’t want to admit it?
Cognac is high quality wine that has been distilled into liquor and put into usually a charred barrel and aged then bottled.
The fact it very old doesn't mean it tastes good.
It might this old because another bottle of out of the same barrel tasted like crap and nobody wanted to open the other bottle. So it sat on the shelf for over 250yrs.