Based on what I've read, Sxmo is not a WM, it's more like a flavored distribution/setup based on postmarketOS. It uses dwm/Wayland as WM, and many other tools to enable other features.
The SSH part claimed (based on my understanding):
1. You can read/send text messages via SSH remotely (say on your computer)
2. Read notifications too
3. Access the Bluetooth devices connected to the phone
> SSH as a first class citizen
What the window manager has to do with SSH?