AeroFS interview questions

Applied online, got a email back with choice to solve either of two questions. I went the extra mile and solved both. Got an email back to schedule for an Skype interview. The interview was with an Engineer, he was really nice, told me about their product and his team and then asked me two algorithm questions. Wrote working code for both and explained my approach; questions were not difficult. The engineer told me that an HR would get back to me. Got your standard "not going to proceed" email next day.

Filled out a coding challenge, got a call back. The interviewer started by asking if I was busy, and if I found this stuff boring. Then he asked me to reverse an array on a code sharing website. After that he asked how I would change phone numbers on a website. He sounded really angry that my solution didn't include regular expressions, and even more angry when I asked what they were (because I wanted to learn). Maybe he was stressed out over doing interviews constantly, I don't know. Either way, I've never heard an interviewer get mad at me before. I didn't get the offer, but maybe that's for the better.