It's the human condition to think like this. We tried x method and were successful; therefore, method x is the right way to do things. No.. no there are a billion ways to do things and method x just happens to be one of them.
I agree, to a point. I've done my fair share of interviews (as an interviewer) with a vast number of candidates, from different backgrounds. With the little data from this experience (on purpose not calling this an "experiment"), I definitely saw a much higher S/R.
In a sense their language choice selects for people who learned something not taught in school.
It also tests for in the worst case the ability to convert Google'ed questions from one language to another. Or a more likely case of writing new code.
The whole process looks like a test with no control experiment (i.e. a set of interviews with a more popular stack).
Don’t get me wrong, I’m quite sure Carlos is an amazing engineer, but I don’t think your stack has much to do with it