[muddyrivers]

I had a very similar experience many years ago. It was an start-up. The interviewer was the ex-CTO of a widely used open source project/product, and led the engineering team in the start-up. Although I regarded myself a good engineer, I was pretty nervous.

After several questions that he was sure I knew the regular stuffs and was qualified for the job, he said he was going to ask some really hard questions to see how much I really knew and what was my thought process. The questions had no simple answers. Each of them required knowledge and experiences from a few technical fields. I didn't know much then. He guided me how to solve the problems, discussed the pros and cons of each approach. Then he told me how they did it, how other products in the same category did it, etc.

The half-hour interview was prolonged to one and a half. At the end, he said, "You have a very intuition on what are the right directions to go when facing unknown complex issues", and gave me an offer. It is my best interview experience. (I didn't join the start-up due to other reasons.)

The technologies have been advanced in a blazing fast speed i the last 10 plus years. Technical interviews, on the contrary, regress in a similar speed.