A man operating a silver 2002 Toyota Camry approached the restricted area twice, though never accessed the plant, officials said.
So this sounds like he was inside the perimeter but potentially not within the boundaries of a higher security interior zone, to me. It may not mean that at all, but if it does it might explain (see my comment above) that they weren't authorized to use force under the circumstances.
Again, I recognize this is just speculation on my part, just explaining my thought process.