I think this would be true if the irrelevant information was within the question, but in this case it is tacked on to the end. Usually when irrelevant information trips up students, it is because it seems like part of the problem. When it's stuck on the end and preceded by "Random fact," as in this study, I don't think it would trip up the students. The only case where it might is if the student is reading the problem in a language other than their native language.

Putting the cat fact at the end of the problem puts it right between the part where the person reads the problem and starts to really think about it. It has the test taker switch contexts and think about something unrelated right at the start of when they should normally begin their problem solving process.

It would be easier to ignore if it were before the problem.

An effect might also happen if you put a fact that arouses strong negative emotions.