> It's fine to be dubious of a claim, and it's fine to ask politely for sources or rationales. Just be nice.
I was not aware that "citation needed" is considered impolite. It is something I use at work a lot when interacting with colleagues. My apologies, I'll refrain from that in future.
Perhaps it is a difference in 'climate' between working in a science based industry where we often get challenged on our data versus software development industry. Maybe I've spent too long in academia where 'citation needed' is an indicator of interest in my topic and considered a good thing.
I disagree, it is in fact a very polite and fair minded way to respond to claim you find dubious. If anything they were being more polite than later in the comment when they suggested the claimed results should be impossible (though that's still a reasonable claim to make if they beleive it to be true).
Rather than saying the equivalent to "I think this cannot be true", a request for citation merely means "I am interested in this claim and would like to know the source" (even if phrased more tersely). The content is more indicative of the intent than the phrasing, and requesting a citation is not an accusation at all, it is a request for a source for further research.
It's fine to be dubious of a claim, and it's fine to ask politely for sources or rationales. Just be nice.