GC just describes a set of algorithms that track and manage resources at runtime. GC-languages would be languages that use a GC for all or nearly-all memory management.

But non-GC languages can absolutely use GC algorithms. It's actually pretty common - Chromium uses GC in C++, for example. This lets you selectively choose where your GC applies and tune it for not just the application but for that specific bit of the application.

There are lots of interesting algorithms for this that solve exactly the problem of "I have a concurrent data structure and I had to swap out a pointer" without a refcount - for example, epoch based collection.