Thanks for sharing this wiki page, I didn't know about it.
The installation works, but I can't connect from 10.0.2.2 with the outside. The network is isolated.
The problems with that wiki page start here: "then run virt-manager to get the friendly GUI to create KVM guest machines"
With the "friendly GUI" it is difficult to describe the steps in a reproducible way. The instructions about qemu etc. (below) are much more friendly than the "friendly GUI", in my opinion.
Any suggestions to fixing the problem?
It is hard to tell, without reproducible instructions, or without having access to the test environment.
But I suspect that you have to enable masquerading on the host. There are some instructions about this at the end of the wiki page.