Per vehicle code and opinion of courts it is an arrest. Do you need the sections and citations?
Officers couldn’t pull you over specifically for a seatbelt violation initially either.
As much “this will never happen” that has ended up happening (across the regulatory and legal spectrum), by the time we get to old Soviet style or Chinese style control with crap like this they will have a nice FAT database of DNA, and when Senator X’s grandchild needs a liver, someone who matches will “have an accident”...
We have this kind of arguement for every kind and level of government crap, and the folks who are all “This is gonna lead to misery and woe” are always right and the folks who are all “Well this might save one little waif from getting buggered by the devils right hand man” are wrong and they keep lapping this sht up...
I would refer you to Terry v. Ohio.
Also, please tell me what law or decision would allow a police officer to take a DNA swab at the scene of a traffic stop....citation please!