When Bishop Heahmund is face down on the floor, praying, he asks that the Vikings be cut down like the "ears of corn at harvest". Corn was a Mesoamerican crop that was unknown to Europeans until after Columbus arrived in the New World in the late 15th Century.
References to "York" are incorrect through this whole story-line. When this was set, York would have been known as Ebacorum (Roman name) or more likely, Eoforwic (Anglian name). When the Vikings conquered Eoforwic they renamed it Jorvik, from which the name York was derived much later. The name York, explicitly spelled that way, was not used until the 13th Century.
The phrase "The king is dead. Long live the king" was not used until the late 13th century, which is many centuries after the events and stories depicted in the series.