If you are financing this property the underwriter will require clear title also. Quitclaim will not be sufficient.
Banks think that they are above the law in some cases, perhaps this is one.
You should consult your Title Company/Escrow Company for legal advice, if not a regular attorney knowlegable in real estate law. Try to get the scoop directly from the Title Company, as they will be insuring your clear title. They should be able to provide you with a "Chain of Title" which tells you who sold the property to who and when. Maybe theres a missing signature somewhere. Who knows. It sounds like he says if you raise any questions, then he has the right to cancel?? If you were my buyer, I would definitely raise some questions. On the other hand, maybe he's just paranoid.
Is this a pre-printed form, or something the seller wrote up? Good Luck. Don't sign until you speak to that attorney or title agency attorney.