Calling someone deaf when they aren't is used when the person doesn't hear the initial statement. This is rude because calling someone deaf just because they can't hear that one statement is biased.
They are being biased based on ability. Asking if someone is deaf because they may not have heard the comment is being discriminatory based on ability.
To correctly answer these questions i would have to have more information on your subject. If you can add more to this so i could help you further it would be great.