I did not know the language stuff (was less familiar on the dates, so didn't notice they were so wrong), but I spent a lot of this episode going "Germ theory wasn't presented until the late 1800s, how the fuck does Ichabod seem to have such a grasp of concepts like herd immunity?" like he seemed to know right away how and why a plague we had never been exposed to in the present would be a big deal, but really probably shouldn't have understood the significance.