I think the article generalizes the author's experience with first line interviews of wholly unqualified people to all post-interview feedback, and definitely shouldn't. People who literally can't Fizz Buzz are not going to argue with you about how no they are actually great devs. People who are borderline candidates who didn't quite get there in a final interview on fuzzier attributes (too slow, spaghetti code, etc.) are a lot more likely to take feedback poorly.

I tried giving post-full interview feedback for a while, but I stopped based on low cost/benefit.