All the while Guinevere is imprisoned, her wrists are shackled, but when Arthur, Merlin, Morgana, and Tom open her cell to free her, the shackles are absent.
When Arthur, Merlin and Morgana go into the caves near the end there are lit wall torches throughout. These can only burn for about an hour so would not be lit already.
Gwen prepares a "sandwich" for her father but this name for that type of food has only been in use since the 18th century.
Gaius tells Uther that "the scientific process is a long one." The scientific method did not arise until the early modern period.
Witches being burned at the stake was not commonly practiced until the early modern period.