Is the story of Abu Basir cited as evidence for the permissibility of fighting without a banner?

Question:
He says: Honorable Shaykh, may Allah grant you success. The Companion who was in the Treaty of Hudaybiyyah fled from the polytheists, moved to the seashore, and began fighting the polytheists, he and the Companions with him. Does this indicate that fighting is permissible without a banner?

Answer:
No, he wanted to escape; he did not want to kill them. He wanted to get away from them. If they had let him go, he would not have killed any of them, because they had a covenant with the Messenger of Allah (peace and blessings be upon him). They were the wrongdoers who held him, and he only wanted to escape from them, to repel the injustice from himself. But if they had let him go, it would not have been permissible for him to fight them, because there was a covenant between them and the Messenger of Allah (peace and blessings be upon him).