You kind of left some stuff out from the middle. He was not free to go on his way immediately; indeed, he was threatened with arrest for not being sufficiently subservient to the cop.
Once upon a time, a police officer could get disciplined for using foul language when arresting a suspect. Now, otherwise law-abiding citizens have reason fear that they will be arrested for solely for annoying a cop.
When you fear for your freedom solely because you're in the presence of a government agent, that is not a free society.
"You kind of left some stuff out from the middle."
I didn't leave anything out of importance. After his response the officer requested that he get out of the car, he ran his information and allowed him to leave.
"He was not free to go on his way immediately"
He doesn't have that right. He was at a DUI checkpoint and didn't answer questions. Very abnormal behavior for a citizen. Officer often pull over suspicious individuals at DUI checkpoints. From stop to go it took 15 minutes. It could have been 5 minutes but he wanted to play ACLU games.
"When you fear for your freedom solely because you're in the presence of a government agent, that is not a free society."
That is simply hyperbole or paranoi. You have free will to leave any time you wish.