It's not disingenuous. You aren't even really ignoring it, you're acknowledging it and not answering, which is the worst place to be in. Some people like to ask stupid questions to get people to have to acknowledge it. You're acknowledging it, but you're not rebutting it. You would've been better off just ignoring it entirely if you really think it's disingenuous, or saying "I don't think you're being honest here."