Firstly, you're not entitled to any job you want just because you wrote Homebrew. If you accepted an interview with Google, then you accepted the fact that Google will judge you based on your problem solving skills, just like every other person was asked.

Secondly, I don't think this is a hard interview question; it's certainly fair. Did you expect to be asked knowledge-based questions that Google knows you're already good at? Questions specifically geared towards you? Or questions where Google can watch you solve a problem and be comfortable with the fact that you are able to solve coding problems? Did you think Google would hire you to write Homebrew? Or solve problems on teams Google has?

I think this person is just being unreasonable.