The fact that it allows separate arguments should make injections vulnerabilities a lot less likely to happen by accident since there shouldn't be any need to interpolate you arguments into the code string (this would also mess up the compiled function cache so you definitely want to do that anyway).

Also, LUA is a very small at core and I don't think it by default includes things like file system access. You pretty much just get what the host applications gives you, which in this case seems to be just the Redis API.