I fixed a small issue in my theme that I’d noticed, where other people’s sites weren’t picking up my author details. The problem? My author info wasn’t included in the entries. I had a site-wide h-card but I hadn’t got it in the entries themselves.
The process for figuring out who has written a post is referred to as authorship, and the IndieWeb wiki page on it is very helpful. Also thanks to Sven for the help.