Not only that, but the only concrete example the author gives is that they asked him about red-black trees. Probing knowledge of data structures is very releva

Not only that, but the only concrete example the author gives is that they asked him about red-black trees. Probing knowledge of data structures is very relevant to day-to-day software development work: even if you don't actually implement them (or haven't since college), having a good knowledge of how they work is the only way to make intelligent decisions about tradeoffs involving them.