Oh I no doubt understood the author's intentions with using feign in that manner. However, that does not mean it was the correct term to use, despite what we may "feel" or "get" from it; nevertheless, troubling ourselves with such a minor detail is really rather ridiculous. Besides, if we go any further, conversation on this runs the risk of igniting a rather banal descriptivist/prescriptivist flame war. :)

The closest term to describe what the author meant is I believe a litote: https://en.wikipedia.org/wiki/Litotes