Well, the police would have a more complete timeline than we do - including store video - which could preclude the possibility of an earlier encounter. I still don’t know how much stock I’d put in an account of an account of an account, though, you know?
IF there was a first verbal exchange, I'm picturing it as having to take place 10 to 180 seconds before the recorded call to dispatch starts. Quick contact, Z is suspicious, TM stays in visual range, Z calls dispatch.
The only reasons this is bugging me is Z's credibility and Serino's credibility. I don't see a first encounter as affecting the ultimate outcome at all.