Very confused researchers
This has nothing to do with languages. They are comparing the performance of compiled programs, runtime environments and/or virtual machines. The garbage collection reasoning is specially poor: C/C++ programs can be designed to run, and can run on a garbage-collected runtime. And if you use fixed memory buffers and other techniques of the embedded programming, you can write complex Java programs that will never need garbage collection and even compile them to native executables. A language is a thing, and a very different one the is runtime implementation of a program written on it. Even if the language has only one.