Oh, Lua's type checker doesn't check function calls at all. Pass too few arguments? The rest are nil. Pass too many? The extras are dropped. An editor could check for it relatively easily (and some do, I think), but the language doesn't care at all.
I'd check for myself but Luau's web demo seems to lack the most important feature of their dialect, type checking.
Since you're here: Is it reasonably feasible for users to add declaration files for code exported from the host application? The lack of documentation got me stuck the last time I tried to embed Luau. Aside from that, I'm very excited about it!
This is just because definition files don't support doc comments yet (for hovers w/ luau-lsp)
Lua has a type checker?