> multiple-return is pretty much unique to Lua (vs. returning a tuple)

Multiple returns are from Common Lisp (I don't know if the history goes back further though), and they aren't tuples. They're the return-position analogue of what are default arguments in argument-position; like default args allow callers to ignore arguments they don't care about, multiple returns allow callers to ignore the return values they don't care about. You can add a secondary return value to a function without breaking existing callers, just like you can add a new default arg.