The situation was predicated on the fact that Roy and his team hadn't grown suspicious of this airplane.
Chris had been controlling the conversation, and so far, Roy had certainly not detected anything unusual; otherwise, he would have ordered his men to fire by now. Although Chris was still in control of the situation, Roy was beginning to harbor suspicions.
The consequence of detecting something off was heightened vigilance, followed by combat. Roy had already started to doubt Chris's identity, and if he still couldn't dispel his doubts, he would have to take some measures, such as demanding that Chris immediately prove his identity—a process that wouldn't take much time.
Chris could not be forced to prove his identity because he couldn't do it. If it came to that, it would mean the deception had been exposed, so Chris had to dispel Roy's doubts.
