It's OK to flag
anything - that's free will at play.
It's especially OK to flag things that are off-topic as per the guidelines:
Off-Topic: Most stories about politics, or crime, or sports, or celebrities, unless they're evidence of some interesting new phenomenon. Videos of pratfalls or disasters, or cute animal pictures. If they'd cover it on TV news, it's probably off-topic.
https://news.ycombinator.com/newsguidelines.htmlas opposed to:
On-Topic: Anything that good hackers would find interesting. That includes more than hacking and startups. If you had to reduce it to a sentence, the answer might be: anything that gratifies one's intellectual curiosity.
There was very little in the linked thread that gratified intellectual curiosity.