It’s not nitpicking at all. Words are supposed to have meaning. Taken literally (which is the only way that words from a 911 operator should be taken), the operator merely stated what he didn’t need. At best, it was a very ambiguous statement. It would have been perfectly reasonable for Zimmerman to respond: “That’s okay, I don’t mind”. For all we know, that’s what Zimmerman was thinking.
I doubt that. I've never made a 911 call, but I'm familiar enough with police policy that, if I called 911 and received that advice, I'd take it as an admonition to leave pursuit to the officers when they arrive. Certainly, George Zimmerman, a wannabe cop who has made 46 calls to 911 since 2004, would have a similar understanding.
Indeed, Zimmerman responded "OK" to the dispatcher's advice. And it seems that, in fact, he did break off following Martin, and he stated that he had lost Martin. But, unfortunately, Martin had not lost Zimmerman and apparently decided to teach him a lesson about profiling and disrespect in an unlawful manner, not considering that the object of his lesson might be armed.