The text says that “the angel of the Lord appeared no more to Manoah and his wife. Then Manoah knew that he was the angel of the Lord.” Manoah knew only after the angel didn’t return. In other words, when the angel ascended in flames, Manoah still didn’t get it that it was the Lord. Only when the angel does not come back does Manoah finally get it. This man's dullness cannot be lost on us.
21 The angel of the LORD appeared no more to Manoah and to his wife. Then Manoah knew that he was the angel of the LORD.