Careful with that line of thinking. There’s a significant body of research showing that people feel like a “chat about tech” interview provides the best signal, but it empirically performs the worst with a roughly 50% correlation to on-the-job performance. You’re better off flipping a coin because at least then you’re not biased.
source: https://en.wikipedia.org/wiki/Noise:_A_Flaw_in_Human_Judgmen...
I was going to point out that a correlation of 50% is pretty good (specially for predicting job performance from a single interview), whereas flipping a coin has 0% correlation with anything that is independent of the coin flip (such as job performance).
You probably meant to say the probability you rank job-performance of two random candidates correctly based on an interview is about 50% (what your source calls "percent concordant"), a correlation of 0%.
Out of curiosity: do you remember which section of the book looks at "chat about tech" interviews compared to other kinds of tech interviews in regards to their job performance prediction capabilities?
The "Improving Judgements" portion uses interviews as a case study and builds up from "just have a chat" to the typical multi-round panel interview with pre-defined rubrics that we see in tech these days. When done correctly, the book suggests this is the best we can do short of hiring everyone and firing low performers soon after.
I remember they specifically mention Google as one of the companies where they ran a study linking interview practices/decisions to on-the-job performance.
Passing a lunch interview should be the easiest thing in the world. Just don't be brazenly unethical or immoral, a complete douchebag, a sexist scumbag or a racist shithead. It's amazing how many people fail at this simple task. It doesn't take a lot of signal to fail.
It's far more important that you can have a civil conversation with a reasonable, level headed person than it is for them to be able to solve fizz buzz in 30 minutes.