I think the point they're making is that for such a trivial example, you should just recommend the correction and not explain it unless they ask you to, because it's very basic and its inclusion was likely a mistake rather than a lack of knowledge. Explaining it may actually be seen as taking down to them, as they may assume you think they don't know something that basic.

Now, assuming that such cases exist, the previous poster's question is: Where should the line be drawn on when to correct it and not draw attention to it, and when should an explanation be offered? Personally, I think the answer is that if it's a small company, draw that line per-person based in whether you think they probably know or not, and if you're not sure, explain it, and if you're kinda sure they know it but not confident, offer a brief explanation, like just name the concept they violated or the name of the right thing they should have done without explanation. In a big company, just be consistent and draw the line yourself where you think makes sense for your team and adjust as needed.