You can't block someone's path unless you know beforehand what that path is.
you like to try to dictate possibilities in a seemingly arbitrary fashion.
we know from previous 911 calls that zimm would talk about how those who he deemed to be up to no good would leave through the back entrance, which is exactly where martin was going because that's where he lived.
it was unintentional, but zimm blocked off martin's path thinking he was heading out the back entrance, he had no idea that was just where the kid lived.