I think they accounted for that, it wouldn't be much of a study otherwise. I am going to guess that they did not ask "How would you defend this position", but rather something like "Can you explain your answer to this question in detail".

In first case, yes the person would play devil's advocate, but that's not really news worth publishing as a study. The interesting part is that when they do it the second way, it basically seems to trigger the mental shortcut where the mind essentially says "oh, I already thought about this question and came up with the answer, there's no reason to think about it deeply again" and simply justifies the answer instead of re-examining the question.

Our minds are much less logical, consistent, or rational than we like to imagine. The concept of cognitive shortcuts is not new, analytical thinking requires effort and energy, so our minds tend to filter out majority of input and process it subconsciously instead of expending energy on consciously analyzing and processing every little decision. Unfortunately the filtering mechanisms are automatic and kick in even for things that should be considered thoughtfully.

Some further reading on cognitive biases and shortcuts: - Motivated Tactician model tries to explain why people use stereotyping, biases, and categorization in some situations and more analytical thinking in others. - Framing) of problem/question affects how we process it, and even the answer we arrive at. - Affect heuristic is "going with your gut", or deciding based on emotion evoked by the question. - Availability heuristic is the "if you can think of it, it must be important" heuristic, which leads people to fear flying more than driving and terrorism more than flying, even though their chances of dying from a car accident are far higher than ever being involved in a plane crash or a terrorist attack.