In CA, just like WA, a DUI can be proved by a .08 BAC or by showing that the driver's ability to drive was "appreciably affected" by consumption of alcohol and/or drugs. The best proof for this is bad driving. It takes about 45 minutes for alcohol to enter the bloodstream. If Marshawn's last drink was more than an hour before his arrest, his BAC would have been higher at the time he was driving than when he was tested.
The questions cops ask during a DUI arrest are intended to commit a driver to his story (how many drinks and time of last drink etc). Best advice for someone who is pulled over is to be polite, have your license and proof of insurance ready, but tell the cop NOTHING. Say that you'd like to speak to your lawyer before answering any questions. Also, decline to take the "field sobriety tests." If you know you are sober (less than .08) offer to take the portable breath test, which is not admissible, but may convince the cop to let you go.