Out of the 4 only one of those weakly applies to what M knew about Z.
Nah. Anyone who jumps out of their car, chases you around, and won't explain himself, is an extremely aggressive maniac at the very least, and very much a threat. "Gun" was quite possible, and may have been known - I wouldn't be shot if this wannabe cop idiot pulled it out quickly. Rachel Jeantel was telling the truth, the jurors fucked up the prosecutors fucked up. And I'm not saying "abolish juries", but it does happen, and it happened here.