The article describes the performance implications of the hash tables storing hashes. That it decides to do so based on examining noexcept() of passed in types doesn't make noexcept a pessimization itself
And, as you can see on the sibling thread where I'm being downvoted, there is an actual pessimization: since a noexcept function requires an eh_frame, it will not be able to tail-call (except for noexcept functions).