I think the suggestion is that people who have less free time might be in more of a rush to complete the test, and that surely affects test results without indicating cognitive ability.
I'd bet they don't consider incomplete tests, and most people I think would just peace out in ten or less questions vs continuing on either uninterested or rushed for time
Why would they rush when they have a specified time limit to complete it that everyone else suffers from? Does having less free time make you stupid? Is Jeff Bezos a brain-dented man as a result of being busy?