Seems like they updated the site recently, so figured folks might enjoy some of the new content. It's been a while since I've visited; been using Figma for a lot of what I previously used TikZ for. However, I returned today because I wanted to generate some diagrams from a fairly large spreadsheet, which seemed like a perfect task for TikZ. And to my surprise, there's a ton of new prior art on the site to learn from :)
I think the images are static, so presumably pre-rendered server-side. The editing & rendering on the individual example pages seems to making an API call to a server, which I think is running this [1].