ML, the cop said the guy wasn't free to leave. The guy was detained. That's actually the very definition of "detained".
You would get that overall impression from the video, but the details show it's a false impression.
In the course of this discussion I've been through the video several times and the first time the guy asks if he's being detained (5:02) the cop says "No, but when we get calls..." and then we hear a long discussion the guy seems egger to have, which is contact. The next time the guy asks if he's being detained the conversation between the guy and cop Horn goes like this as best I can make out given others in the video are also talking at the same time. If you disagree, check it out for yourself.
14:54
Guy: Am I being detained or am I free to go?
Horn: Get with your father and go.
Guy: No, am I free to proceed on foot?
Horn: No you're not, because...
Guy talking over the cop: Okay, what are you charging me with?
Horn continuing his answer: ...because you are causing a disturbance to the public you're disturbing the peace...
Guy: Okay, I'm willing to continue with him (father)
The guy accepted Horn's explanation of why he couldn't continue on foot. That's not detention. The guy was free to go with his father, but not free to violate the local ordinance of disturbing the peace. That's like being in the median and asking a cop "Am I fee to go" and the cop saying "go to the traffic light and cross there" and then you say "no, am I free to cross here" and the cop saying "no you're not because that's J walking" and then you saying "okay, I'll go up to the traffic light and cross there". That's not detention.
If you assume the guy was knowledgeable about the law then his quick agreement to go with his father shows that he believed the cop was right about the local ordinance. Disturbing the peace ordinances are highly subjective and some may want to argue that the guy wouldn't be disturbing the peace had he continued on foot. I'm not going to argue that point because it would be a "what if", as the guy did not challenge the use of that ordinance on the video, so it's irrelevant.
Bottom line, there was no detention at any point in the video, only contact.