Not only should you not answer questions at a traffic stop, you should never talk to the police under any circumstances.
It’s not just the US, more laws get passed everywhere making more individual behavior illegal. It’s just too easy to catch you on something.
Police interrogations aren't like normal conversations. Even if you're innocent, if you misspeak it goes on the record the way you said it. Think about how many times you've been in a normal conversation and had to go back and clarify something you just said. Your friends are going to give you the benefit of the doubt; a prosecutor can use that kind of thing to make it look like you're changing your story.
There are countries in which your refusal to answer questions can be a factor in determining your guilt at a later trial, so you have to answer questions. But that's not a good thing.
And if you did brake a traffic law, recieve the ticket. Say hey officer, sorry about that thing we both know I just did. If they probe further or try to search your car then stand your ground.
The guy had the right to remain silent, and he exercised it appropriately. Usually the people in these stories do boneheaded shit that earn them their outcome.
He admitted nothing, so they brought in the dog and faked the results to justify a search. At that point his testimony doesn't really matter-- the dog gave them probable cause to search. He did everything he should have done in this situation, including standing his ground-- unfortuantely your rights have limits when the cop you're dealing with is bent.
The only boneheaded thing he did was to sign the waiver, which very clearly stated in bold letters that he was relinquishing his rights over the money.