Stores have no right to state ALL their customers are shoplifters. They must have a reasonable suspicion that a theft occurred to detain someone. They otherwise have no right to search.
This guy’s demeanor or motivation does not enter into whether or not he stole, which, he indeed, did not. They never stated they believed he stole anything...they only stated he refused to let them search him/his belongings...and they had no reason for doing so.
If you don't follow the policy of the store regarding product check, I believe that to be reasonable cause. If you just want to exercise your libertarianism, you should shop at non-totalitarian stores where they don't give a damn if you steal and raise prices.
Store employees have the right to detain and make citizens arrests. I know some one who has done it dozens of time and successfully testified about it in court.