The gap was too large to ignore

For each test image, a system could submit five possible labels. It counted as wrong only if the correct label was missing from all five. This measurement is called top-5 error.

AlexNet's top-5 error was:

15.3%

The next-best entry scored:

26.2%

Lower was better. The difference was 10.9 percentage points on the same hidden test. It was a large measured gap under the competition's shared rules.