In what way is the battle between King Arthur's men and Sir Mordred's men a result of a misunderstanding?

Mordred was a former Knight of the Round Table who tried to wrest the throne from King Arthur while he was on campaign. Before the imminent confrontation, both parties decided to hold a meeting to resolve the conflict, for which they were summoned in a place with 14 men each. On the one hand, King Arthur recommended to his men not to believe in any word of Mordred and in case of any threat, to attack. Mordred, on the other hand, made the same recommendations to his men and the meeting went smoothly. The calm disappeared when a poisonous viper bit a knight in the foot and he reacted with his sword, which was seen as an act of aggression on the part of the other side and the battle was unleashed.