Thank you for sharing! Based on your last sentence I think we're in agreement that it's probably not great to give someone unsolicited advice (but it's fine if we disagree). I wanted to throw out a couple more thoughts:
I think that having experience in the business (or not) is important. I think that sometimes giving advice on an area that one doesn't have experience in can be a weird way to put oneself in a 'one up' position. Kind of a "Look, I don't even do your job, but let me tell you how to do it better" kind of statement.
I'm not saying that this was your intention or your effect but I think it's something engineers are prone to - I know I've done this. Wasn't there even a name for this? Something about "dinner party advice"? If this rings a bell for anyone I'd appreciate the help about this.
Sometimes I've found that if I have experience in the area I can suggest a small change with a substantial benefit (because I've actually done this enough times to know that the advice will actually help, actually) but even there I'd be really hesitant to offer unsolicited advice.
And, as an added bonus, consider that they may have already committed to what they're doing. In which case, even if you're right, you're basically telling them that they've done something wrong - maybe they can fix it (with more effort and/or money) maybe they can't, but that's gotta be an extra burden for them.