The aim of the post was to talk about how to make the stakeholders of your site aware of performance. I do not cover technology at all and this is intentional because technology choices are a completely separate concern.
As the post states, the Guardian site is being loaded on a slow 3G connection on a iPhone. The purpose of this was to show the different kinds of performance but its worth noting 4 seconds under those conditions is not slow. A slow 3G connection in Web Page Test is 98KB/s which means in 4 seconds in optimal network conditions your going to only be able to download 392KB. The reason I test under a slow 3G connection is that this is likely the worst case for most of my users. Also discussing user agent is irrelevant, a responsive site is progressively enhanced you should never consider targeting a specific user agent.
On a side note, I would be proud to be a Wordpress developer (I am not), their community is amazing with the sheer amount of effort that goes into extending out the platform. Of course the CMS has flaws but I can’t fault the community around it and the amazing thing they achieve.