Not the person who originally replied to you, but the HR class I took in college broke down the correlation of interview performance to job performance into a few finer-grained buckets than just structured and unstructured. Sorry, no sources here, as I've since gotten rid of that textbook.

Structured vs. unstructured are the fairly general categories, but that correlation number is accurate. The best predictor I can recall (~0.6 IIRC?) is a "work sample test". You can Google that and find all kinds of HR resources about it.

That is HR jargon for, in this case, writing code to solve a real problem under normal conditions for that company. That is, on an actual computer, not on a whiteboard, and not being constantly scrutinized throughout the process.