His email makes little sense, but who cares. It's his team.
And in his defense, he has 2 NCs and 37 CCs and has played around 4,000 games...so he is significantly more experienced and successful. There have been times when I'm simply too busy to set my lineups in a timely fashion, or I just don't care enough during the 1st season with a rebuild to do much with it since I know I'll lose every game anyway. But letting the AI pick my starting lineup seems like the worst idea I've ever heard.
Your initial email could have probably been a little more polite, but I wouldn't necessarily consider it rude. Regardless, I wouldn't worry about other people's teams, even if I used to coach them. And I certainly don't hand out unsolicited advice without expecting to ruffle a few feathers.