This is a classic of misconstruing correlation and erroneous inference. Certain types of arrhythmia are more common but these are a natural side effect of training. Drinking coffee or alcohol, light exercise or even sex can lead to the same arrhythmia. This is only a problem if you already have some kind of underlying heart condition, where the arrhythmia is a result of the heart condition and not the exercise regime.
Which is why there is zero proof of actual health problems, and endurance athletes are several deviations healthier than the average. Endurance athletes have a lower risk of heart problems, despite a slight increase in some arrhythmia, because the 2 just aren't linked.
Furthermore, most amateurs could only dream of training 30-40 hours a week. even a dedicated runner is unlikely to consistently train over 12 hpurs
there are plenty of papers out there demonstrating a link between endurance sports and AF, I guess it is going to just derail the thread if we carry on as no doubt you can cherry pick some other paper with a sample size of 60 and try to show that this is wrong...