I agree with your second sentence, but your first sentence is pretty profoundly incorrect. Each of its 413 pages is divided into two columns. I generated a random sample of 10 page numbers associated with column numbers as follows:

>>> import random
>>> r = random.SystemRandom()
>>> [(r.randrange(1, 414), r.randrange(1, 3)) for i in range(10)]
[(299, 1), (164, 2), (292, 1), (246, 2), (205, 2), (113, 1), (167, 2), (393, 2), (16, 1), (129, 2)]

Page 299/413 column 1 contains: part of a confused description of mathematical optimization in the sense of finding infima, incorrectly conflating it with space-time tradeoffs in software, which is at least a software engineering topic; and the beginning of a section about "multiple-attribute decision making", which is almost entirely about the kinds of decision-making done by corporate management. Though software design is given lip service, if you dig into the two particular "design" approaches they mention, they turn out to be about corporate management again, with concerns such as brainstorming sessions, identifying business cost drivers, staff headcount, presenting ideas to committees, etc. Conclusion: project management, not software engineering.

Page 164/413 (6-12) column 2 is about corporate operations (for which telemetry can be used), corporate operational risk management, and automating operational tasks to improve corporate efficiency. Conclusion: project management, not software engineering.

Page 292/413 (15-3) column 1 is about software engineering economics, specifically proposals and cash flow. Project management, not software engineering.

Page 246/413 (11-12) is a table summarizing chapter 11, which contains both project management and software engineering elements. I'm going to eliminate this point from the sample as being too much work to summarize fully and too hard to avoid interpretation bias.

Page 205/413 (9-13) column 2 is about software engineering management issues such as the difficulty of estimation, the project risks posed by the rate of change of the underlying technology, metrics for managing software, and what software organizational engineering managers should know. Project management, not software engineering.

Page 113/413 (4-14) column 1 is about what a platform standard is, TDD, and DevOps. Mostly software engineering, not project management.

Page 113/413 (6-15) is another summary table page similar to page 246, so I'm eliminating it too.

Page 393/413 (A-5) column 2 is about the SWEBOK itself and the documents it draws from and contains no information about either project management or software engineering.

Page 16/413 (xv) is part of the table of contents, so I'm eliminating it as well.

Page 129/413 (5-12) column 2 is about random testing (software engineering), "evidence-based software engineering" (an utterly vapid section which contains no information about software engineering, project management, or anything else, as far as I can tell), and test cases that force exceptions to happen (software engineering). Conclusion: software engineering, not project management.

So of the seven non-eliminated randomly sampled half-pages in the document, four are about project management, two are about software engineering, and the seventh is just about the SWEBOK. I guess my declaration that it's just a set of management practices was incorrect. It's only mostly a set of management practices. It's not at all only a small fraction.