Precisely. It's easy, and intellectually lazy now, to claim he acted stupid. We all can look back at past actions, and determine what we could have done better. That's how we learn so much. Based on everything we've been privy to, Zimmerman acted with a conscious effort to simply keep an eye on someone he believed was acting suspiciously, until the police he had contacted, arrived. This belief was validated by how he was subsequently attacked by Martin.
Yes, had he stayed in his car, Martin would likely be alive today.
It can also be said, that had Martin not attacked and beating Zimmerman to a pulp, he'd still be alive today as well