I think there is a word that means something is presented or said without context, like a statement that appears random. “Leftfield statement” comes close, but I think there’s something more concise.
Some people malapropriate “non sequitur” for meaning this. (I’m basically looking for the word that means what those people think “non sequitur” means.)
I’ll give an example of what I would describe with the word we’re looking for:
Someone on Twitter posts the message: “Oh, not this again…”
No context (e.g. in previous tweets), completely leftfield.
A possible word choice here is impertinent.
It’s a good starting point, because its meaning in English has shifted over time from irrelevant to insolent and now (partly) back to irrelevant again. As a result, it has picked up an impressive collection of synonyms.
Thesaurus.com leans towards the insolent meaning, but from there you can broaden out to other words.