Actually:
1. The statute reads: (3) A person who is not engaged in an unlawful activity and who is attacked in any other place where he or she has a right to be has no duty to retreat and has the right to stand his or her ground and meet force with force, including deadly force if he or she reasonably believes it is necessary to do so to prevent death or great bodily harm to himself or herself or another or to prevent the commission of a forcible felony.
So, it applies to anyone, not just patrols.
2. Nothing is obvious. It is completely possible that Martin saw him following him, so whirled and attacked him. It is completely possible that Martin was really out hunting hispanics. It is completely possible that zimmerman was out hunting blacks.
3. zimmerman did call 911.
4. You don’t need to call 911. It doesn’t matter what the author says, the law is not ambiguous.