Okay, I've edited the page to hopefully make it more clearer. Feel free to improve it. However, most of the page is autogenerated by the api help itself, which would require code changes to improve the documentation.
Actually, A, B and C are "correct". Redirects are a tuple of redirect source and redirect target, and this api is supposed to return that list, but not always. It depends on the parameters. The title refers to the redirect target, but if you make it return the ids, those ids refer to the redirect source.
The best way to see how it works is by testing the api itself.
If you check Special:WhatLinksHere for Project:About, listing only redirects, you get currently 13 results.
The same results you can get using the api
with from and to = About, and namespace Project (not very useful output), and the same as generator (the output is the same but titles reflect redirect source instead of target).
Note how "About" in the filters doesn't include the Project: namespace, because it's included in the namespace filter. Adding the namespace manually on the title filters will result in an error (!)
But this usage is not very useful, because that's what API:Redirects returns. The only usefulness of this api IMHO is using it as generator, with "from" and "to" pointing to the same page (a bit awkward), or setting the "unique" parameter.