Ok.
I can see your confusion and I sympathize, at the same time and as you can see above, redundant can be used in a way that is not wholly synonymous with superfluous.
To wit, redundant applied to the subject at hand could mean #includes that are repeated; as is not an uncommon usage, for example:
Redundant, used in that sense, draws a clear, if subtle distinction with superfluous; for instance an #include that is merely extraneous, as opposed to duplicative. Support for this parochial usage of superfluous in this sense is also extant.
If we apply our faculties for discernment fully, we would see that the OP is specifically referring to the use case most precisely defined as superfluous, (although, I do not deny that being superfluous always carries an unshakeable taint of redundancy).
Moreover, the usage is not purely pedantic; the logic for a tool designed to root out just duplicative includes instead of extraneous includes could diverge greatly; namely the in the former case one could merely scan #include statements and without further investigation into their contents, be determinative.
Penultimately, and by way of an excuse, I would like to note that in my original post, the word superfluous was intentionally emphasized.
And as is evident, the language mirrors your statement in my rejoinder, clearly intending to make the distinction between the two adjectives (to which you very astutely were aware of, at least on some level )
Finally, and IMHO, when we are presented with such clues, we should do our best to indulge our conversational partner by striving to look for their intended meaning with an earnest effort; and avoid the temptation of issuing a reflexively puerile response.