I don’t think it’s a US American thing per se. Refried beans are a common staple of Mexican dishes and may incorporate lard (as will more authentic flour tortillas). They’re mashed, not whole beans.
And while I wouldn’t use them in tacos, canned baked beans like those you’d find in the UK may also not be vegetarian.
Is this a joke I’m not American enough to understand?
The word tacos implies Mexican food, and Mexican preparations of beans traditionally use lard as the cooking fat.
I don’t think it’s a US American thing per se. Refried beans are a common staple of Mexican dishes and may incorporate lard (as will more authentic flour tortillas). They’re mashed, not whole beans.
And while I wouldn’t use them in tacos, canned baked beans like those you’d find in the UK may also not be vegetarian.