I think that was just a way to ethically cheat the fast...In southern Germany they got around it by wrapping the meat in a dumpling (Maultaschen), so that god wouldn't notice: "The Swabian German nickname for the dish, Herrgottsbescheißerle, means "small God-cheaters""
https://en.wikipedia.org/wiki/Maultasche#History
EDIT: just remembered another similar cheat, where beavers were defined as fish, allowed to be eaten at lent.
I think illustrations or stories from the middle ages are to be taken as symbolic or allegorical rather than factual like a biology book would be today. They wrote down a story not because they necessarily believed it be factually true, but because it taught a different kind of truth. For example, no one has ever believed that Red Riding Hood actually happened or that you can cut open a wolf's stomach to pull out a living person.
You can guess that now in the 21st century, but we're talking about illiterate peasants who never traveled past their nearest market center. It's naive to assume we can even possibly empathize with their epistemological outlook.
For example, just look at the medieval sources about barnacle geese from the 13th century (from the educated class):
> Barliates, as Aristotle says, grow from wood, and are birds which the common people call 'barnesques', having a similar nature. [1] (I chose a short quote to make a point but please read the rest of the source, it's hardly an allegorical text)
They didn't have the concept of falsifiability or anything even remotely resembling the scientific process (or critical thinking, for the most part). The literate were obsessed with the classics and just took Aristotles and Ptolemy's word for everything, until Copernicus and Kepler had their way. Anything resembling scientific knowledge filtered down to the peasants or came from old wives tails entirely.
Even now with almost universal literacy we have a significant fraction (if not majority) of the population believing in ridiculously stupid nonsense like astrology. I don't find it hard to believe that people thought that geese's life cycle included barnacles.
[1] https://www.medievalbestiary.bestiary.ca/beasts/beastsource1...
Please, can I have that for my typo collection?
There’s a similar story about how rabbits in Japanese use the classifier 羽 (-wa, “wing”) normally utilized for birds, instead of the 匹 (-hiki) you’d expect for small animals, because Buddhist monks really wanted to eat them and thus declared their ears to be wings. I don’t know how historically accurate that is. (I’m also assuming this has to come from Chinese and thus likely also has a counterpart in Korean, but can’t prove that with a cursory look through Wiktionary.)
Medieval Science was Baffled by Birds - CuriousCabinet123