Funny enough, it’s a bit of both. The msys2 runtime is a fork of the Cygwin runtime, and they keep parity pretty well.

https://github.com/msys2/msys2-runtime

MSYS2, rather, which often seems to be bundled with a hybrid mingw install, but itself is based on a patchset to the main cygwin DLL and generally is a 'saner cygwin'.

To be even more pedantic, the Unix tools that come with Git for Windows are MSYS2-based, not MinGW-based, and MSYS2 is more like Cygwin than it's like MinGW (it's Cygwin with a few patches.)