That statement is pretty much antithesis to everything anyone has ever said about hiring amazing engineers...What's ironic is, a Rails interview test is actually best for people who are willing to learn Rails and demonstrate that they can solve your problem with your tools. It's not really great (and potentially offensive) for people who will most likely be able to pass those tests in their sleep.
You shouldn't be hiring people because they have experience that matches your tech stack solely because they'll kick ass on the first week.
You should be hiring people that will kick ass 3 weeks in, and a year from now, and 5 years from now -- regardless of whether or not they currently have competence in the nitty gritty details of whatever libwidget you use at this exact moment.