But not bailing your ass out to tend to other things isn't a mistake. Failing ganks mid/bot and other things might of, but his choice to fix your problem isn't.
Really from my limited knowledge of the game his only mistake was raging at you, but sounds to me like you were pointing a lot of fingers in games from his comment.
In all honesty it's not sound rhetoric to create an argument without also mentioning your faults, which I didn't do. I recognize that. However, he still should recognize his mistakes. If he doesn't then that's on him and I feel sorry for anyone else who loses games because of his mistakes.