Responsiveness is one of the more modern (as in wasn't a thing 10 years ago) somewhat advanced parts of webdev and just not in everyone's portfolio of skills. There is a skill level where it's possible to handcode a perfectly functional website, but miss most of the modern best practices.

Huh! I didn't even notice that it isn't until I saw your comment.

Looking back at it again it feels quite comfortable to zoom in and read/scroll. But maybe that is just my phone being the right size (it's an S9).

I'd say the page is mobile friendly in a sense, even though it's not responsive.