It looks like the “demo site” (really just Marcelo’s web site) is not actually using exactly the same Marfa theme anymore. It’s similar, but he has customized it, especially the home page.
For the Custom home page instructions, if you want a completely from-scratch HTML page you can create the layouts/index.html template but without the define "main" part which is what adds the header/footer and other styling. That 2-pane home page would need to be custom, though, since it’s not built into the theme itself.