I don't think when someone is talking about a "closed device" they usually mean "closed source". I at least took it to refer to whether you can run whatever software you want on that device+OS, and how easy it is to do so.

I think Windows is up there with the open source OSs (Linux, BSDs, etc) on regular PCs are at the same end of "run anything you want from wherever you want it", iOS devices are at the other extreme of "only run things approved by Apple", Android devices are pretty closer to iOS because they make you jump through hoops and potentially lose access to various functionalities to install certain things or gain root access. Modern macOS, as far as I understand, is somewhere in the middle: you have to jump through quite a few hoops to install certain kinds of software, and a few aren't permitted at all I think (unsigned kernel modules?).

I think the keynote here is the closed/open hardware.

You can run Windows almost on any hardware. So it is much more open in general.

You can equally run almost any imaginable software on both operating systems (if we ignore the performance), but you have extreme difficulties to run macOS on most hardware.

You said "equally as closed Windows machines."

In terms of the machine Windows is way more open in that you can use what hardware you want. But yeah the software is closed source.