Either bad interviewer ( focused on syntax rather than problem-solving skills), bad day, or simply this:

> people would do amazing stuff despite failing basic algorithmic tasks. That's what makes hiring decisions so hard.)

It's important to note that this doesn't mean algorithm tests are inherently broken. People who can't solve _basic_ algorithmic problems tend to be weak employees. Rejecting them screws your recall (a few would be amazing if hired) but tends to improve the precision a lot, so the trade-off is often worth it.