This seems like something you could and should have caught in the moment, without having to use your feedback technique. If they answered, and only mentioned the high-level tests, and you expect them to have low-level tests, then just ask, right then, if that was all of their tests, rather than silently assume the worst and move on.

Heuristic: if a remark seems outrageous, double-check before making a major decision on it.[2] This is not just in interviews, but life in general.

Example: Your friend says "Hey can you toss me through the window [of this skyscraper]?"

Your version: Call their family and 911 to report them as suicidal. Give a long speech about why they shouldn't kill themself. Then explain why you did what you did and ask if you misunderstood anything.

Sane, heuristic version: You reply, "You... want me to throw you to your death?"

Friend: "Oh jeez, no, that's just an expression we use here. I want you lift me up onto the balcony."

[1] Quoted in full:

>I gave one candidate feedback along the lines of “when you explained the app that you built, you talked about the testing that you did at only a very high level, so I’m worried about your depth of testing knowledge, particularly around Test Driven Development (TDD)”. The response was along the lines of “Oh. You’re right. I didn’t really delve into detail, but here’s how I went about doing the testing and here is my general approach in other examples”. The candidate then went into significant depth explaining how they had done TDD over the last 10 years, which clearly demonstrated their understanding and maturity of the practice. Misunderstanding corrected.

[2] Which, to be clear, you are doing by using your technique ... it just feels oddly delayed and lets a misunderstanding accumulate much longer than it needs to; my example is an exaggerated version of the failure mode.