I'm sure the guys who shot him did a background check before deciding to chase him down.

A private person may arrest an offender if the offense is committed in his presence or within his immediate knowledge. If the offense is a felony and the offender is escaping or attempting to escape, a private person may arrest him upon reasonable and probable grounds of suspicion.

This is the law that matters. Did the people stopping him have a legitimate reason to believe that Ahmaud had committed a felony in their presence. That's it. I'm not going to speculate on what happened either way, I wasn't there, I'm not a cop or a lawyer, nor do I have any evidence beyond excessive reddit screeching.