Yet if you're old enough to have gotten started in the time of JavaScript in the late '90s, or QBasic in the early '90s, or systems like the BBC Micro or TRS-80 in earlier decades, you should know what the author's talking about.
Everything you need to program is just there. It just works, there's no extra installation, you start a program and start coding. And just about any PC has what you need. [1]
Nowadays you can technically develop on any PC with a browser by locally editing HTML / JS / CSS using Notepad, but it's rather painful. How hard would be to have a default Firefox environment for budding coders? These days you can probably do some Wasm magic to create an entire Linux OS in a browser tab, and install stuff in a virtual disk in the local storage.
Heck, it probably wouldn't be that hard to cobble together the existing pieces to make a Firefox addon to do that.
[1] Granted BBC Micro and TRS-80 weren't PC architectures, but for computers of that generation, a built-in BASIC interpreter was pretty much expected.