One of the language results doesn't make sense. It claims that it matters, significantly, if you solve interview problems in Java when the hiring company is a Java shop, but not when the hiring company is a C++ shop.
But that's reversed. It is in fact fairly difficult for a high-level language programmer to pick up C++, and facility with C++ (or at least C) is a common, accepted goal for C++ hiring shops. A C++ shop that hired candidates without regard for their aptitude at C++ would have real problems.
The data suggests that it is easier for a C++ programmer to get make a good impression in a non-C++ shop, than at a C++ shop where they likely to test you on C++ edge cases.
Interesting that this effect does not show up for Java programmers.
I think this makes sense, because C++ is seen as this difficult beast. Non-C++ shops will be impressed that you know any C++, while a C++ shop will want to dig much deeper and make sure you are sufficiently advanced at the language to do the job. Non-C++ shops won't dig as deeply (either because it doesn't seem relevant -- you're not going to be using C++ anyway, so you just need to show programming ability and not C++ mastery -- or the interviewers don't know C++ well enough themselves, since they don't use it in their jobs) and won't ask you about in-depth edge case language features (because why would they if they don't use the language), but in a C++ shop, they will care about all of these things and have people who use C++ and can ask in-depth questions.
Why isn't it the same in Java? I'm not sure, perhaps its because Java has less gotchas as a language (certainly a lot less undefined behaviour and weird memory-related gotchas, no templates, no multiple inheritance etc) and C++ has this "its a difficult language" prestige which Java doesn't have.
They give P ~= 0.36 to this claim, in an article that I think makes more than 1/0.36 ~= 28 claims, so I would suspect that maybe that's just a coincidence in their data?
But that's reversed. It is in fact fairly difficult for a high-level language programmer to pick up C++, and facility with C++ (or at least C) is a common, accepted goal for C++ hiring shops. A C++ shop that hired candidates without regard for their aptitude at C++ would have real problems.