It's just a traditional name -- much as one might refer to a woman as a "lady". Etymologically, the word "lady" is connected with bread: it means "loaf-giver". But no-one nowadays expects that a woman will give you bread just because you refer to her as "lady".
Current U.S. usage seems to accept "tallow" as name for high-quality beef fat, but whether that's a recent language change or something that might also have been so in other English-speaking societies in the past I really don't know. Historically, tallow seems, as far as i can tell, to have been used for more nondescript fats -- the sort of thing you might use for greasing a boat, an axle, or a church bell, or send for candle-making.