look its a story, it creates a setting, has a certain athmosphere, and it usually focuses to make its main plot believable or entertaining in a way. how he failed to accurately portray that arrows cannot actually fly up a 700 ft wall and stick into something in our world is irrelevant for the plot, it is irrelevant for the story, and if you fall over that then imo you are nitpicking. and yes after all he's just a human being he does not have knowledge about everything, i doubt that if he realised these things when he was writing he wouldnt have changed it.

and because it is a story and you have a plot which has to be told, therefor sometimes you have to make concessions and if that means that reality will be amongst the casualties then so be it. hence a 14 year old kid can wear full battle armour because it makes for a better story.