How to Derail an HN Thread

I came across an interesting observation in a rising Ask HN thread (https://news.ycombinator.com/item?id=6999429).

The question asks about FizzBuzz equivalent tests for other fields. But if you go check out the comments, all you'll find is one person's answer to the actual question, and rest of HN arguing about the answer to the commenter's response and its explanation.

Why do you think this happens? The question is FizzBuzz level of difficulty and there's no physical or external reward for the right answer. But the question managed to derail the thread so hard, that everyone seemed to forget the original question entirely.

Are we trying to prove something to each other or ourselves? Or perhaps our inner geek just can't stand to let a question go unanswered? How many days in the 21st century have dates in which the numbers of the month and day add up to the last 2 digits of the year (1/2/03, 1+2=3)?