We know that TM had four minutes before his final confrontational act in which he didn't run/walk/crawl back to the condo where he was staying after getting suspended.
We know he didn't call the police (or his father or Eric Holder, Jesse Jackson, Al Sharpton...) for help, (or for fatherly, legal, or spiritual advice) in those four minutes.
We do know that GZ abandoned his surveilling of TM after losing sight and headed back to his vehicle.
We don't know why TM, a minor, didn't just go "home".
We do, and the author does: This malignant new ["new"?! Denial is not a river...] form of black culture plays a dominant role in defining what it means to be an authentic young black male.
Actually, we don't know that. It fits the known facts well, and it is probably what happened, but it isn't itself a known fact.