Depending on where you are, and their interpretation of "prompt" the police officer could have been in the wrong. Canada requires officers to inform you of the cause of your detainment immediately upon being detained. The logic is the government has to convince you to submit to the arrest/detention. If they do not, you still have 100% of your rights.
From my understanding after reading about this a bit more, US doesn't have the same definition of "prompt" and the officer could delay it like he did in the video. Some states will require him to inform you immediately though. That officer should have handled himself better and by denying that request, he not only escalated it, but opened his department up for lawsuits and if the suspect was charged, gave a chance for those charges to be overturned.
BTW though, many police officers, especially down south, get paid near minimum wage, especially if they're working for a particularly small county.