Legally speaking, being pulled over and detained by a police officer is not the same as being placed under arrest. Police officers are authorized to interact with people on different levels depending on the reasons. For example, an officer can always start a casual encounter, can briefly detain you to ask questions or investigate further if they suspect you of a crime or infraction, run a check of your license, and even search you under limited circumstances. These types of examples are not considered being under formal arrest but rather being detained. And as they say, the devil is in the details so it is primarily what information an officer has at the time that determines the level of detention. A formal arrest is not free to leave, being taken into custody, cuffs on, triggering Miranda Warnings, etc. So if the officer was trying to place your friend under arrest when he resisted, he could be charged with a crime.
If a reasonable person would understand that they are not free to go, the reasonable person should pretty much do what the officer asked him to do, rather than acting like a toddler. Disobeying a reasonable request from a LEO is asking for charges for resisting arrest. Will those charges stick? Hard to say. The Cop may well have been having a terrible day, but your friend needs to understand that when any LEO says "get out of the car" the only reasonable response is "Yes, OK, I am getting out now". This is not a consent to search, it is common sense. Also, your friend REALLY needs a lawyer now.
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Yes, if being pulled over for a traffic offense, under Washington law it's an arrest. It's not a custodial arrest, but it is an arrest. As for being told to step out of the vehicle, you should do so since you have no right to refuse. Being asked to step out does not mean that your friend is suspected of a criminal offense, but if your refuses then your friend is likely to face greater problems for the refusal than for the act that led your friend to be pulled over.
This answer is given merely for informational purposes and does not create an attorney-client relationship. For specific advice, contact an attorney in your state to see if working together makes sense.