Then I'm not sure why you said "to be fair[...]partly undocumented".
Isn't the thing you being fair to the last line of mrguyorama's comment? The one that was blaming the user? The thing you replied to was an argument over the appropriateness of that specific line.
"To be fair" because neither "it's documented" nor "it's undocumented" capture the state of things. I'm highlighting why someone would consider the API not fully documented to make it easier for others to see mrguyorama's point of view, even if I disagree with it. In other words, I'm steelmanning their argument, since I think it was poorly put forward.
It's only steelmanning if that's what they meant, and I don't think that's what they meant.
Trying to strengthen an argument by finding a way that a word could technically work, but not with the original implications, isn't very helpful. I'd even argue it hurts clear communication in a situation like this.
Isn't the thing you being fair to the last line of mrguyorama's comment? The one that was blaming the user? The thing you replied to was an argument over the appropriateness of that specific line.