Even without the concept of an IQ test the fact that if you were given two people who both answered 50 questions correctly, one person took a full day to complete the questions while another person answered them in all in 2 minutes. Clearly our conceptual intuition of intelligence says the Faster person by literal definition of "intelligence" is more intelligent.
Like what is the experiment in this article measuring here? If it's comparing people who got the exact same test scores then the experimenter can't identify differing levels of intelligence because everyone got everything right. How can they say the faster person is stupider then the slower person if the scores are the same?
The only way to truly compare is to find people who got the answers wrong, but in this case your measuring the speed of arrival at a wrong answer which is in itself a pointless measurement.
Obviously wrong answers are faster to come up with and obviously a person with more wrong answers is going to be faster and stupider then the person with right answers.
That said I'm pretty sure reaction time and "clock speed" are part of intelligence, just correlated well enough that you don't need a reflex test added onto the paper test.