Completely different. Git bash is based on msys which is a suite of Linux/Unix tools ported to compile and run natively on Windows. This is taking actual Linux programs and running them as-is on Windows. Wherever the Linux programs make system calls to the Linux kernel, etc. there is a shim layer from MS that translates those calls into Windows system calls. It's not going to be 100% perfect compatibility with every app, but will probably support a lot more stuff than msys.