Just found a story glitch in ghost of tsushima

While riding on horseback along with lady masako during the conspirator quest (tale 8), she mentions that lord shimura was the one who cut the head of whoever killed kazumasa. However as we later find out, tenzo is alive and kicking on iki island. Was this a missed glitch that could not be retconned or was it a bluff playing into the character of shimura who would kill someone else for the glory?