In law it is the defense who is supposed to argue the amount is too much, and the plaintiff should ask for as much as possible because at that point it is punitive. Second, while you may not feel threatened by any single interaction with police, this officer was angry and had to have exhibited aggressive behavior. These ingredients have resulted in lots of interactions going south.
Thirdly, let's put you in this man's position, we will make one assumption - that you know flipping a cop off is settled law and protected free speech. You're driving home and you get pulled over. For what? You were just driving and not speeding, what gives? "Licence and registration. Do you know why I pulled you over? Because you flipped me off". This is not a first level offence. This isn't being on your phone. This isn't driving without a seatbelt or speeding. This isn't driving erratically. This cop just told you he's going to ticket you because you flipped the bird, but you didn't. You try to explain you didn't and he's going to get mad because you called him a liar. Now you have a citation in hand and you try and NOT swear and actually flip him off. He has deprived your freedom of speech and given you a ticket for it and you know it. If you're gonna get a ticket you may as well do the crime right? So the officer, rather than writing another citation you know will get thrown, has your car towed. He settles you with a $300 tow AND a citation OVER A GESTURE that he is legally and constitutionally WRONG about, and you know he is. He then arrests you for it, and you spend an hour at the precinct settling this. Then when you're free to go, you have to bum a ride to go get your fucking car. A month or so later, you have take time off work to go to court. You miss making probably another $300 because a day off. It gets dismissed because it's a first amendment issue - you knew this would be the result all along. A minor feeling of vindication because you are now out $500 for missing work and other legal fees, maybe an Uber to go pick up your car, and have been harassed by a state patrolman, spent an hour in jail instead of whatever you were driving to go do. 3 years later the ACLU says "hey so you were right, and we want to sue over it. Would you NOT say "yeah fuck that dude" and sign on for it?
Minor footnote, he won 100,000, and 75,000 went to the ACLU