I also thought it rather strange, but it appears to be quite ancient, certainly more than 7000 years old. Hey, if you don't have grapes, then you have to find something to ferment.
The Proto-Indo-European Goddess of drunkeness is named Ekwamedha, which can be translated "horse mead".
If you handle it right, then you can end up withcurds of silids and a highly alcoholic liquid.
There are a number of recipes on the internet, so I won't bother linking to any.