Who wants to bet that at some point after the closing of the site, they switched over from a live CMS to a static copy of the site and in the process of doing so things got a little screwed up when exporting data from a MySQL database with the different encoding weirdnesses that can sometimes occur with MySQL and how the db schema was set there.
Yeah this really looks like an encoding issue during migration.
I've run into similar problems when moving old content between systems, especially with MySQL and mixed encodings. It can get messy surprisingly quickly.
If you used UTF-8 then you can probably fix those pretty easily. UTF-8 is sufficiently structured that it’s extremely unlikely for a string that’s written in another encoding to be valid UTF-8 by accident. If you write some code to try decoding as UTF-8 and set that as the encoding when it succeeds, you’re unlikely to damage anything in the process.
My blog suffered the same, and going through loads of old pages to check and fix them just isn't worth the effort.