[afiori]

It would almost surely be fair use to include a snippet of code from a different library in your (inline) documentation to argue that your code reimplements a bug for compatibility reasons.

In general it is not fair use if you are using the material for the same scope as the original author[0] or if you are doing it just to namedrop/quote/omage the original.

It is possible to argue that a snippet can be too small to be protected, but that would not be because of fair use.

[0] Suppose that some Author B did as above and copied a snippet of code in their docstring to exlain buggy behaviour of a library they were reimplementing. If you are then trying to reimplement B's libary you can copy the same snippet B copied, but you likely cannot copy the paragraph written by B where they explain the how and the why of the bug.