This practice (adding a ? to a declarative sentence) is very informal, and so you wouldn't see it used in published English language media, so I'm not surprised that you may never have encountered it. It's used as a shorthand method of inviting clarification when the author is unsure of the veracity of the claim.

This sub-thread reminds me that there are many informal rules in languages that are rarely taught, and which can trip up non-native speakers. Informal shorthands, idioms, slang, etc.

It's like a written form of Uptalk.

https://en.wikipedia.org/wiki/High_rising_terminal

It is, but it came of as criticism to me, because using the question mark this way is quite common here on HN and elsewhere.

It seems to be a rather recent phenomenon here on HN (broadly speaking) and for me it falls pretty much in the same category as other overly familiar and rude language patterns such as 'AF' (short for 'as fuck') or 'tho', 'cuz', or 'w/' instead of 'though', 'because', or 'with'.

There is a rudeness in making it one of these faux-questions filled with implications instead of clearly stating what it is you want to say.

I apologize heartily for offending you, that is not my intent.

You did not offend me(with the first post) and I did not downvote you. I just explained, why you received negative feedback - basically missunderstanding. But talking about missunderstanding: I understand your last comment as snarky, unwarranted sarcasm. This I would downvote.

FWIW, does not read sarcastic from the sidelines.

And as mentioned elsewhere, the entire thread seems like a good natured discussion: perhaps it felt different without the original "edit".

Everything about this exchange seems fine to me. You asked a clarifying question about an “advanced” usage of the question mark, and you were answered with a neutral description of what’s going on.