That's why they could not see any other scenario besides their own incorrect one. If they had, they would have been "wrong" and they would have nearly seen two boys endangered because they were not paying sufficiently close attention to three boys roughhousing in the pool.

Young children may scream "I wish you were dead!" at their parents but don't "mean" it even though they also do. Your mother and her friend used the "intentionally" in the same manner; you would not have had an adult's intent, you were trying to "win" or were angry at your brother, etc. something of that nature is probably what they thought? You did not drown your brother (in their eyes) so using such strong language is in the "almost doesn't count except in horseshoes. . .and hand grenades" category; in your case, the hand grenade one because you knew the truth and they did not and their lack was hurtful to you.