Premisconception

The act of making an incorrect assumption, occurring before the person speaking has even made the point.

Can also be applied to answering a question that wasn't completely understood.

George had a severe premisconception about Jills request for time apart and started talking about another vacation.

Edgar had several narcissistic personality traits, including a tendency to premisconceive what anyone would say, making large leaps back to his own concerns and complaints.