I'm guessing the author's website is misconfigured. Every path except the root returns an HTTP 404, but the 404 page loads some JavaScript that fetches assets based on the URL. For example, the ThinkPad blog post loads https://utkarshsingh.xyz/assets/thinkpad-p14s/thinkpad-p14s....
This mostly works, but some browsers will display a warning or their own 404 page. Also it means his site won't be indexed in search engines.