The first thing cops would have asked him was “What did he look like?” The second & third would have been “What was he doing and where did he go?”
The “What was he doing?” part is murky at best. Most have TM just walking along. I don’t think a statement by Mr Z has been released saying just why he thought TM was acting suspicious. Do you have one?
In a majority minority neighborhood it would not be unusual to see a black youth with a hoody walking around - night or day. Just that would not cause Z to focus on TM.