> Being accosted by a threatening looking
> guy at night will do, no?
tl;dr: no.
Again, please look more closely at legal definitions which are not some kind of arbitrary thing made up by a guy at the other end of a keyboard: the principles of self-defense are the codification of thousands of years of practice. You cannot simply attack someone and later claim self-defense unless you've exhausted all of your options.
I don't know what you mean by 'accosted' -- no one presented evidence that Z attacked M, or that Z was even the kind of person who might attack a guy he was following. What we do know is that once the physical part started, Z was no match for M physically. The defense provided physical evidence of the position of the two men when M was shot.
You keep changing your story, and you're down to tiny threads. Under no theory, nor under any evidence collected or presented, can you say that Z was not entitled to the self-defense claim because he provoked the use of force against himself.
What I think happened was that Z bugged M enough that he thought he would simply beat him up, and did not count on the fact that Z had a gun and was able to use it.
People do get beaten to death, you know.
http://www.nbcbayarea.com/investigations/Berkeley-Man-Near-Death-at-the-hands-of-CHP-206494311.html
(random result from searching google for "beaten to death")
/jordan