Before artificial sweeteners, people satisfied their cravings for sweetness with natural products, including honey or dried fruit. Raisin wines, made by drying grapes before fermentation, were particularly popular. Historical records show these wines, some known as passum, were enjoyed in the Roman Empire and throughout medieval Europe. The most famous of raisin wine of the period was Malmsey, with varieties of this type produced across the Mediterranean.
I don’t think they replaced the sun-dried raisins with honey, otherwise the honey taste would be a bit too strong, too obvious. Instead my guess is that they used it as an additive in the final product, if the resulting passum was too dry. Because:
*you can do this at home with some grape juice. Even the unfermented version is delicious, it becomes syrupy (andgreat on vanilla ice cream).