I ran their developer version on an old Nexus 7 for a while, and it was more like the latter (Windows analogue). There is still a full terminal experience available even on the phone as I understand it, just a lot more proprietary software.

All Ubuntu mobile devices are running Unity 8, which is the next version of their desktop period written in Qt set to replace Unity 7. Currently they are still shipping Unity 7 on the desktop, though. Whenever desktop Ubuntu gets Unity 8, it would be able to shrink the screen down to a phone-like UI if you shrunk the display.

At one point, in the not too distant future, the mobile version will become the "full" Ubuntu version.