In situations such as this, it is really hard to say whether you should file or not. Some banks file because the transaction is out of the norm or established pattern of the customer; we do not file solely based on this factor. Unless I had some background knowledge or facts to support my filing or a gut instinct that told me it was suspicious, I don't know that I would file in your case.
Also, one of the things I teach (and basically beat to death) in all of my BSA trainings, is that front line staff should ask questions. Using your scenario, if I were the teller the first thing I'd ask would be something along the lines of 'are you buying a new car?' or any open-ended question that would help me understand what the large withdrawal was for.
If we don't teach front line personnel to ask questions and actually communicate with our customers, that leaves personnel responsible for BSA monitoring and filing with a lot of questions such as yours. And needless to say, it makes our BSA lives quite difficult at times.
"I shall permit no man to narrow and degrade my soul by making me hate him." ~ Booker T. Washington