Based on a comment by @ruud@lemmy.world it looks like they're just using a docker container, only takes seconds to update. He said he'd probably set up Watchtower which auto updates containers so it should be only an hour or so behind.
When you're using vger hosted on a different domain, your password has to be read by them and sent to the Lemmy server to log you in.
If it's on the same server, the pw stays in the one system (albeit it might still need to go through the two pieces of software, idk how it's configured).
I assume the idea is to give people an easy and nice looking default mobile experience for lemmy users without users having to go find things like wefwef/voyager themselves.
Wefwef is an an web app, like an app, but that runs powered by your phone's web browser, usually accessible through a URL and you can then install it.
m.lemmy.world is just a page, hosted by lemmy.world. Typically, it should have just had a mobile view of the usual lemmy frontend. But what this announcement is saying is that Wefwef was made the official mobile frontend for that website, and thus, going to that page will show you the contents through a wefwef view.
Also replace all places where I wrote wefwefs with voyager, since they rebranded.
There is no difference, itβs two websites hosting the same software. The idea I think is to use wefwef as the mobile view for lemmy.world, since you can also use it straight from your browser (the beauty of a web app!).