Criminal Investigations: Illegal Traffic Stop

My question involves police conduct in the State of: California. While travelling at a legal speed in a brand new Mercedes 430i convertible rental car with the top up at 11:45 pm I got pulled over. I had broke no laws and when I inquired to the police why he stopped me his only response was I let you know in a minute. I asked quite a few times during the stop as to why I was stopped but never was given a reason. During the stop my passenger was searched and arrested for possessing a load firearm by a felon with proirs and possession of controlled substance. The police report stated that the officer had recognized my passenger in the dark, seat on the far side of the car, through a 5% tinted window on the cop SUV, and hadn't seen that person in over 4 years as someone that might be related to drugs. However, He also stated that he saw me and recognized me from over 8-9 years ago without any direct contact until that stop. That is after he had a full on conversation with me about not actually remember who I was but I only looked familiar. They also stated in the report that they were in the area we arrived in due to reported gun shots. The only reported guns shots in that area were 2 days prior at 3 am and the case had been close the same morning at 11 am accourding to police records. Our stop was also labled as an "Other Agency Assist." Had it just been a traffic stop wouldn't they had labled it as such in the crime reports? The officer walked to the passenger side of the car and saw who the passenger was prior to returnung to my driver's side to greet him by last name only. If it makes any difference I know he should not had had those things on him I was unaware until that point. We had just returned from a comedy club.
As far as I know to pull a car over the police need a reasonable suspsion of something illegal about to happen, just happened, etc. They aren't supposed to be able just to pull people over just because they might know who someone is. My friend was not wanted for any crime or violation of supervision. He is on probation however, until they pulled us over and saw it was him they wouldn't have known that. My tags were good since a brand new rental car. Same goes for the condition of the car, no lights out nothing missing, nothing hanging anywhere. And I drive over safe and follow all traffic laws because I dont want to get pulled over.
I am just wondering if this stop was legal from its inception
I do not believe the officer in question knew who was in the passenger seat do to the details: the type of car, time of night, dark window tint on the police car, and traveling speed while turning a corner, after quite a few years without contact. Based on the conversation with me, he surely didn't know who I was. Nor do I think it is legal to just pull people over without some type of reason. So far everything the report said was the reason sounds like lies. And they never once answered durring the traffic stop as to why I was stopped.
So does anyone thing that this was a legal stop or am I missing something?


Thanks for your help and time.

Criminal Investigations: Illegal Traffic Stop