You can "work for another company at the same instant you're working for [your current one]"? What about a direct competitor? Do you actually get paid per job

You can "work for another company at the same instant you're working for [your current one]"? What about a direct competitor? Do you actually get paid per job worked, and not salary? How does that work? What metrics do you use to determine the amount of work done? This is a genuine question. Most setups like this I've seen are with freelancers, and those are contractors.