I knew an INTP on this forum who once thought he was an ISTJ, anyone remember his name?
My hypothesis behind any N thinking that they are an S is largely due to a misconception about the meaning of S and N. N does not imply S-tard. (And, conversely, S does not imply N-tard.) Simply because one is not literally blind does not at all indicate an S preference. Ns are humans. Humans use senses. (barring rare conditions and afflictions) Therefore, Ns use senses. It's more than reasonable to expect that an N can mistake themselves for an S due to a misunderstanding of N. (and perhaps S as well)