This is why they would humor cell phone guy, IMO:
1. In case there really IS a guilty 30 year old black man out there; their first priority at this point is finding ANY clue to lead them to Hannah.
2. In case they do have suspicions about cell phone guy, but are not sure. If they put out info about this other guy and NO ONE comes forward at all to say they remember a guy matching this description, it becomes more likely that he was fabricated.
1. In case there really IS a guilty 30 year old black man out there; their first priority at this point is finding ANY clue to lead them to Hannah.
2. In case they do have suspicions about cell phone guy, but are not sure. If they put out info about this other guy and NO ONE comes forward at all to say they remember a guy matching this description, it becomes more likely that he was fabricated.
Why would L.e want to throw a sketch into the mix, to confuse the public even more, if they knew or thought it was really the other guy?