QuickTime for Windows existed long before then, and Apple ported a bunch of the old Classic Mac Toolbox to Windows as part of that.

IIRC it was actually this Windows port of Toolbox that in some ways laid the foundation for Carbon - i.e. a port of the Toolbox API to what became Mac OS X.

Interesting stuff, I wish there was a way it would get open sourced one day.

Yes, this is correct.

I do remember it had its own font rendering which looked out of place on Windows.