I understand JJ's mother's frustration, but from the legal side of it, I can understand why this was not released back when it was first found.
PD likely received this footage due to time/proximity to where his car was found (I'm guessing thats where this took place? considering car found on 26th and this shown to mum on 27th), and thought the man might be Jelani just due to his appearance. I doubt they saw anything else 'suspicious' on video. When mom confirmed this wasn't Jelani, he was just a random citizen who was uninvolved in the case, just physically in the area, and there would be no legal reason to release his image.
Now that Jelani's body has been found and foul play is now on the table, this man can be treated as a potential witness (I doubt he's considered a POI or anything like that) due to his proximity to the location and his behavior. Perhaps he saw something strange and half-heartedly tried to use a neighbor's phone if he doesn't have a cell? idk