Yes, seems like the GitHhub repo was a bit of an after thought:

Top right:

> About > SOURCE CODE for "Database Performance at Scale: A Practical Guide (Apress, 2023)," by Felipe Cardeneti Mendes, Piotr Sarna, Pavel Emelyanov & Cynthia Dunlop

But readme.md:

> This repository ACCOMPANIES Database Performance at Scale:A Practical Guide by Felipe Cardeneti Mendes, Piotr Sarna, Pavel Emelyanov & Cynthia Dunlop (Apress, 2023).

[ my emphasis ]

In the context of technical books "source code for" often means "source code for [readers of the book to reference while reading]" rather than "source code for [building the book]"

I disagree. Words have meaning. 'Open source' means 'open source' in all contexts.

For comparison, https://doc.rust-lang.org/book/ is an open source book. A PDF with a CC license without a repo of the publishing artifacts is not an open source book. It's just a free book.

The question is not whether it's open source, the question is what it is.

I wondered about that, too, but in the body of the article they claim the license is a Creative Commons flavor so I interpreted it as a marketingdroid faux pas that the source is not available but that the content is open

I guess the distinction would be if someone wanted to upstream a change, not fork it, through what mechanism would that take place, but I'm going with "highly unlikely" on that one