Ask for two different self-evaluations, an official one that can be used to give himthem a raise and an unofficial one that can be used for self-improvement. Make sure he doesn'tthey don't confuse the two. In the future, try to intercept histheir official self-evaluation if possible, just to make sure hethey understood you.
But don't try to deny histheir observations. They're probably correct. People who are at the top of their game are extremely critical of themselves. That's how they're able to improve their skills year after year.
And if your own boss, or if HR, has already seen histheir evaluation, try to walk it back and try fight for histheir raise as much as you can.