Open source contributions aren't as useful for a hiring decision as you imply. Did the candidate spend several days working on a small change? Does the candidate only do quality work when it's something that is personally interesting to them? If yes to either of those then they might still be a bad hire.

Don't get me wrong, I love to see open source work, it is a plus and it definitely helps paint the picture of what the candidate is passionate about. But just having impressive open source work alone is not enough to make the technical interview unnecessary.

> and ace the technical interviews

If there's an IQ test after they ace the technical interviews, then that's a really weird order to do the interview, but I don't think that's the situation that the above comments were talking about.