I can tell you, however, that it's quite common for Rails programmers to not know much about Ruby except for the parts used by Rails. In the U.S., Ruby was popularized by Rails, and very few programmers learned the language separate from Rails. I'm unusual in that I picked up Ruby first (while visiting Japan) and learned Rails much later.
Rails is much more than a DSL - I would call it a framework, which includes several DSLs as sub-components - but for a pretty broad range of the complexity of your web application, you spend more time and code dealing with Rails library functions and DSLs than with 'pure' Ruby. In most cases, that's the point - Rails is useful precisely because it gives you library functions, DSLs, and middleware components that deal with common web app issues. Rails is a good framework precisely because you can use the framework instead of building things from scratch in pure Ruby.
Because of those factors, many Rails programmers don't know the underlying language of Ruby or understand it very well, and I think it's accurate to say that a common mistake made by Rails programmers is to misapply Rails-style conventions in other projects.
Rails programmers do have a reputation, in some places, of not being good programmers. (Whether the reputation is entirely accurate is another issue.) I think the most common specific complaint I've heard is that Rails devs don't know SQL because ActiveRecord does it for them.