First of all, they didn't say they are referring to the UI.
The main element in a web browser's UI is the web view where web pages get rendered. It may look the same 'rectangle' as it used to look 10 years ago. But the way chrome renders web pages and execute JavaScript have undergone a lot of changes over the years. Also they have added a lot of new standard and nonstandard HTML, CSS and JavaScript features. Then, there is WebGL 2.0, WebAssembly, WebGPU, etc.
The main element in a web browser's UI is the web view where web pages get rendered. It may look the same 'rectangle' as it used to look 10 years ago. But the way chrome renders web pages and execute JavaScript have undergone a lot of changes over the years. Also they have added a lot of new standard and nonstandard HTML, CSS and JavaScript features. Then, there is WebGL 2.0, WebAssembly, WebGPU, etc.