No. He's a work-for-hire at best if he's not an employee. Works for hire keep rights unless they transfer them in writing. If he wasn't paid, there's insufficient consideration to support any written transfer, or he could avoid any such writing through recession. I could allege several ground here, including fraud β they never intended to hire. This is a scheme for free work.
In the alternative, he was an employee and this company is using the interview process to circumvent employment and wage laws, which is actually a better position, because they've probably done it to hundreds of people and they'd probably pay good money to avoid it being brought to the court's or state's attention. How you present that is a tough dance though. You have to avoid committing blackmail.
