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.
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.