If you take a dozen people of different backgrounds and ask them to rate a statement like this by how much it "attacks someone's character" or is "emotionally unsafe", you're going to get a whole spectrum of responses.
Likewise, you'll find similarly varied responses to how and whether character judgment makes someone afraid to speak up, and how and whether a organizational demand for "emotional safety" makes for a more or less comfortable workplace.
This is the sort of stuff that people really mean by "culture fit" in organizations and especially on intimate teams. You and the person you're responding to probably wouldn't thrive in the same work environments. That's okay, though, because there are a lot of work environments and (among skilled craftspeople with job mobility) those of us who recognize these cultural differences have the insight to seek the right orgs/teams for ourselves.
First, you have to be right. Saying "we suck at that" if we are good or even just so-so is counterproductive.
Second, you need a foundation of trust. People listen to negative feedback most when delivered with shared interests.
Third, it has to be delivered to the right audience in the right forum. People who are unable to act on it should not be included.
Fourth, it needs to be oriented in a positive direction. It can be negative. But the goal is improvement, not degredation.
Fifth, it has to be clear. Clarity and specificity are effective.
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These things are nuanced, and without being in the situation, it's effectively impossible to judge what is done the right or the wrong way.
It's just a colloquial way of saying "I've earnestly thought about X, Y, and Z and think it's the most effective way path forward" or "my intuition is telling me X, Y, Z is the best way to go"
It's a way of expressing that they have a strong sense of how to proceed and the "passive-aggressive jab" that you hear is just an artifact of the idiom not being familiar or natural to you.
Can’t really tell which situation it is without more information but both are common
I suppose if it happened regularly enough, and it was clear the founder usually spoke from a position of ignorance, I'd eventually disengage and start to dismiss them out of hand, but I can't say I'd ever take it personally.
While the founder could just as easily have said "I think we should do X, Y, and Z" instead, I'm more than a little concerned at how easily someone would shut down over the original statement, which strikes me as mostly harmless.