In this particular case, I received ~20 resumes for 1 job and 80% were not Ruby-only resumes. So yes the Ruby-only screened them out. However I would have gone back and contacted them if none of the other 80% of candidates worked out.
It just means: don't select people for their getting-a-new-job skills. Those skills aren't relevant to software development work.
It would be helpful to know more about what you do versus what you don't.