Perhaps a more complete explanation is needed here ...
Fire testing of wall assemblies focuses on the wall keeping the fire on one side - that is, the unexposed side of the wall may not exceed a certain temperature during the test. The side of the wall exposed to the fire is typically completely destroyed within the first half hour of the test.
There are additional standards for things like the plastic used in electrical boxes. One of the tests is pretty straightforward; a sample has one edge briefly exposed to a flame, to see if it ignites ... and, if so, what happens when the flame is removed, and how fast the flame progresses up the sample. Pass this test, and the material is considered 'non combustible,' at least as far as the NEC is concerned.
