But then they say:
You have to be completely comfortable with:
* Developing Ruby on Rails applications
Now, technically they don't say you need to know Ruby, but I'd be rather surprised if you don't need experience in Ruby to be completely comfortable with developing Ruby on Rails applications.You don't need experience with Ruby specifically, you just need to be able to "pick up a new language faster than your laundry" and likely have experience with a similar language. If they interview a candidate with a decade of experience in Perl, Python, and Java, but no experience with Ruby, that would be fine as long as he is a fast learner who would be comfortable adapting to Ruby.
The way I read it is that you don't have to have experience in Ruby on Rails, you just have to be able to learn it quickly and be comfortable developing applications with it. As a seasoned .NET or Java developer, it might only take you a few weeks to adapt ("you can pick up a new language faster than your laundry"), even if you have never used Ruby on Rails before.