The dispatcher said: “we don’t need you to do that” (follow Martin). Not only is than not an order — it’s not even advice. It is just a statement of what the dispatcher believes he, and the police need.
A 911 dispatcher (and other police officials) should use plain, unambiguous language. There shouldn’t be much room for misinterpretation. If the dispatcher had said: “don’t do that” — then that would be a clear command. If he had said “I advise you not to do that” — that would have been clear advice not to follow Martin. Instead he said: “We don’t need you to do that”. It would have been reasonable for Zimmerman to respond: “That’s okay mate, I don’t mind.”
And even if the dispatcher had given a clear and unambiguous "order" to Zim (which he did not), it is my understanding that Zim was under no legal obligation to follow such an "order."
You must follow a policeman's order if you yourself are being stopped while under suspicion of committing some legal infraction. However the police cannot otherwise "order" you do to anything. That's my understanding.