...They disappear if you don't use them.
"What illegal activity do you suspect me of?"
"I have no idea."
"That's not probable cause."
"Right now sir, I'm pretty sure you're a terrorist. [laughter]"
A few things...
I'm not sure if he is required to pull off the road for secondary inspection. But by staying on the road and blocking traffic, he gave them an incentive to let him go. Off the road, this may have gone on for hours. He could have pulled off the road, submitted to secondary inspection, and sued for harassment after they found nothing since there was no probable cause, but how successful that may have been is in doubt. Note the numerous attempts to get him to say that he wasn't going to move. Had he said he wasn't going to move, he would have been obstructing traffic, which is against the law. Instead he insisted he wanted to leave, but was being detained by them.
He knew he had to stop, and stopped. There was no probable cause beyond that, because refusing to answer questions is not probable cause. If he had answered in any way, the agents could use their experience to determine whether or not he was lying, but not on a refusal.
At the end where he was asked to provide a drivers' license, I'm not sure if he was really required. Whenever you are operating a motor vehicle, you are required to provide the license to (state?) law enforcement officials (possibly also proof of insurance, registration). But I'm not sure if federal border patrol agents have the power to demand to see his license, and I'm not sure if they can detain him at a border patrol checkpoint, and then ask him to provide his license for operating a motor vehicle. If those troopers the BP said were on their way arrived, he would have had to provide his license and registration, but I'm not sure how you transfer custody of someone being detained for a BP checkpoint to a traffic cop. They could have had the cop pull him over after they said he was free to go, but then the cop needs PC, and then he'd only be required to provide his documentation, and demand his ticket.
Also, note the repeated lies told to him by border patrol agents. There is no legal requirement for them to tell citizens the truth, it is the citizen's duty to understand the law, and act within it. The agent accuses him of interfering with a federal investigation, which is a felony. Were that the case, they could force entry, arrest him, and charge him with that crime. They did not. Note the agent attempts to put words in his mouth, "So you're refusing to show valid ID?" A lack of answer, or an affirmative answer results in probable cause. Note that questions were answered with questions, this is a common tactic because the agent doesn't have to answer questions, but their authority implies that you do. Technically, "Am I being detained?" "Are you a US citizen?" Could be repeated for hours. If the citizen attempts to leave prior to being approved to leave, he will be arrested for fleeing a detainment. The last little part where the agent is "just trying to make conversation" is still questioning. There is no "going off the record" in this conversation. I'm guessing this was the last tactic recommended by the agent's superior before telling him to leave.
Did you notice the little scoff at the end? "Did you get the idea to do this from checkpointusa.org, sir?" First he's a suspicious character, then he's trafficking contraband, then he's a terrorist, then they ask if he got the idea from a web site that talks about American citizens refusing to submit to these checkpoints? He knows he's legal. They know he's legal. They're just wasting his time so they can measure their authoritative penis. They basically admit it at the end when they say their superiors feel that they have better things to do than play this game with him. That's how they view this person exercising his rights. As if he's playing a game, and they want to play right back.
At the end of the video he is told he is free to go, and confirms he is free to go, but he is not allowed to leave because the agents were standing in front of his car. At this point, he could have called 911, and told them he was being falsely imprisoned by officers who specifically said he was free to go, and he feared for his life. If I tell you that you are free to leave a room, and physically block the exit, and refuse to move, that is imprisonment.