This is incorrect - you can run base64 bookmarklets without network. It is running a highly stripped down version of Presto. Opera Mini did use 'server side rendering' while this is handled on the device.
Twitter’s mobile site, for instance, is looking pretty good.
That surprised me as I wondered just how much JS capabilities the browser has; then I realised that article was written in 2013, when Twitter was still relatively sane and not the bloated SPA it is today (yet the actual content being displayed is not much different from 10 years ago.)
https://grumpy.blog/en/nintendo_dsi_browser/