That 90% only measures images already known to be one of CIFAR-10’s ten classes. There is no “none of the above,” so even a perfect benchmark score would still force a calculator into one of those labels.

yep: https://en.wikipedia.org/wiki/CIFAR-10

"The 10 different classes represent airplanes, cars, birds, cats, deer, dogs, frogs, horses, ships, and trucks."