Since the good scholars, experts in their craft, have no idea, any guess is good so long as it is based on what information is known. The people who copied manuscripts were almost exclusively lifelong devotees of monastic life. Their monasteries were largely self sufficient. They produced their own food, their own clothing, their own inks and paint, their own vellum. Any excess was used to trade for what they could not produce such as gold and gems to adorn their books. There was little interaction with regular members of the Church hierarchy or with the nobility so their knowledge and understanding of these two groups was limited and as full of holes as their grasp of how people lived and dressed in the Bible times they illustrated and the sort of plants and animals that filled the Earth beyond their borders. They absorbed tales from travelers but mostly learned from everyday experiences and from what they found in the books they copied. Armored knights, traveling about the Christian kingdoms, were romanticized and their exploits were related to the struggles all Christians faced against a hostile world. To me it seems that the knight battling snails could be a metaphorical indulgence of the scribe, free to indulge lonely fantasies while spending his hours in lonely devotion to holy work, picturing himself as a valorous warrior for God engaged in war against the slow moving tedium of daily life and preserving the work of ages against the ravages of mindless consumption and decay.