I'm not sure that follow most people's interpretations. Wikipedia[1] even asserts it's usual use in response to statement that are "deceiving, misleading, disingenuous, unfair or false". Personally I see it used, and use it myself (sparingly) when responding to someone you think is knowingly misleading you (possibly in jest). I would be offended if anyone but a close friend called my statements bullshit and I believed them, as I would interpret that as an accusation of me intentional misrepresentation.
1: https://en.wikipedia.org/wiki/Bullshit
> I say there is no authoritative root source of this information.
Sure there is, in the instances I am (and have been) referring to. That doesn't mean it's infallible, but in the absence of a third party witness or evidence to the contrary, sometimes all you have is the statement of the person about themselves. The only way to find a fault in those situations is for them to admit it. Related to what we've been discussing, I'm not sure I would distinguish between a lie or a mistake when someone recants immediately after a statement and questioning of said statement when in regards their own actions in the way we've been discussing. I consider both acts of bad faith (if someone puts so little thought into their words that they must recant at the slightest questioning, then I view it as not better than a lie).