Hi I'm one of the people that worked on the webdesign, back-end and hardware. You are right about the caching, one of our strategies is actually to cache very aggressively. Not only for images but even for all HTML aside from the front page and about pages. This works for us since low-tech magazine only publishes a maximum of one article a month and the site spans a decade of content which won't change anymore.
However, since we were still working on the site at the time it got massively popular, we changed the caching settings in order for people to see the changes and fixes that we were pushing.
[0]: http://www.lowtechmagazine.com/2018/09/how-to-build-a-lowtec...