A few kinds of coffee processes remove the cherry by allowing it to ferment, which can create alcoholic/boozy flavors in coffee. I don't speak German but I did a bit of a deep dive on honey processes in Costa Rica and apparently "black diamond" honey process takes 22 days or more to ferment the cherries slowly (this roaster is probably sourcing from the same or a nearby farm). Also, having the warm water sit in the grounds probably accentuates the fermented/funky/wine-like smells. Next time you taste that coffee, try and see if there is any whiskey flavors or smells.

Side note: whiskey/fermented grain mash is a recognized coffee flavor note in the World Coffee Research Sensory Lexicon as well as smoky flavors you might expect in a bourbon.

It is also common to age coffee in bourbon barrels as others have mentioned.