In many ways it is...for example, my employer will not hire anyone who has been arrested. They do not care if the charges are later dropped, or no charges are filed.
My guess would be to arrest the driver/owner of the car. Common sense would state that if there was a large amount of money in the glove box, and a stash in the back he would know about it.... however, I would still like to know why they searched the car for speeding first.