This exact question turned up in reference to the Sandy Hook school shooting. A few of us asked why it was so prominent on HN given then guidelines, and in particular I said:
Yes, this is important, yes, it's newsworthy.
No, it's not "Hacker News". It's all over the
news, and there's nothing specific about hacking,
or start-ups. It's not even of "deep interest"
in any real sense. It's tragedy, pure and simple,
and then it becomes politics.[0]
PG replied (in reference to the guidelines you quote) with:
Note those words most and probably.
Another accused me:
Try on a little human emotion and sensitivity for
size: this isn't your site to police. Even pg has
pointed out the precision of the wording which you
seemingly ignored.
I usually stay out of discussions about on-topic/off-topic now. There's nothing to be gained. I just flag things according to my own criteria and move on.
[0] https://news.ycombinator.com/item?id=4922380