http://www.sanfordfl.gov/investigation/docs/Twin%20Lakes%20Shooting%20Initial%20Report.pdf
I don’t see anything about going to the store in the police report you linked. I think there are questions about this store trip, the first of which is what store? There are a lot of fragmentary statements floating around, such as that he was getting snacks for his younger brother, and of course that this was at halftime of the NBA All Star game. Then we see it stated that the father was not alarmed when he did not return all night. So lots of questions.
Also though, being in between the buildings seems to indicate that Z followed him in there. This does not contradict the statement attributed to him that he didn’t see him and turned to leave but it would seem to be a form of pursuit. ( The building locations are easily seen in Google Maps in the Retreat at Twin Lakes complex. )