Either that page was a mistake of the Kakashi Gaiden page was a mistake. I believe it was that page though, Minato was only Hokage for like a year or so.
both of them have to be mistakes, minato didn't become hokage until after the obito incident so why was his face there when obito was telling that ho bag rin his dreams of being hokage?
actually it`s the other way around.the question is why is there a minato`s face carved in the rocks.minato became hokage after the war,after obito supposedly died