Without forcing one thru a Cloud server....if I can express it that way.
Let’s try this a different way.
Arm is a supported architecture for Ubuntu. I even have a version of it running on my BeagleBoard (Much like the Panda ES mentioned in the article).
It has Firefox, it has LibreOffice, etc. Everything that compiles for Ubuntu can be in any architecture that Ubuntu supports!
If you have the compiler and libraries and drivers - it all plays together. That exists for lots of different ARM platforms.
They start from source code for Firefox, or LibreOffice and compile it for the different architectures. These things were built to run with X Windows, and the ARM Ubuntu systems support X - so they all work.
Does that explain it?