With the wormwood, maybe it is an early version of absinthe?
When I first read their boner last night, I looked up ancient european starch or something like that, found some papers about it, and wormwood was just one of the source plants (others included wheat, which is used to make starch in Europe today, along with the more common corn) used to make starch. Since they were always looking for food sources, figuring out processing and prepping foods, and finding ways to get high, it’s not unlikely that they discovered a few of the properties of wormwood. Absinthe makes the heart grow fonder, btw.