It kills the bacteria that produces it, but that is a good point. Still, it might be possible to test for it, and its unlikely that restraunt food contains it just from getting spoiled.

As I understand it botulism is mostly a concern in canning. If you kill most of the bacteria but the botulism bacteria is hardy and survives and produces it for months in the can.

You won't get that from eating spoiled buffet or even garbage.