Benjamin, isn’t that what the discipline of semantics seeks to understand?
It seems there’s a change in word meanings in the world of plants and horticulture and so forth. As a botanist 50 years ago, I was trained that an annual is a plant that can complete its whole life cycle in one year. Seed to flower to fruit/seed again. Biennial takes one year to store up as much food as it can. The next year it puts up leaves again and makes as many seeds as it can, and is done. And a perennial requires an indeterminate amount of time to mature
enough to make seeds. And then makes seeds for many years.
Now when I go to the nursery people say it’s an annual when they mean that the
local winter will kill it. Let’s take the case of geraniums in the climate of their origin, they live and bloom for years and years and years. A perennial. In a climate with a freezing winter the winter kills it and if you want geraniums next year you plant them again. (Or like a good
permie, bring them in, propagate cuttings indoors over the winter)
In the killing winter situation there are nurseries who call that an annual. I got frustrated one day and said so if I was asking about olive
trees you would call them an annual because I’d have to replant every year. ( I’m not always a popular or polite person!😉)
So as for why people would call a fava bean perennial… It comes down to what do they mean by perennial, and what’s happening in their garden.
Without standardized terminology, you just have to ask “what do you mean by perennial?”
By the terminology I was taught, whether or not a person lives in a climate so mild the winter doesn’t kill fava beans, they can go from seed to seed in one growing season, and that makes them annuals.