The author and people who insist on teaching (just) that "a branch is just a ref" fighting over the wrong point. The important part is to understand that each commit is itself both a complete snapshot of the repository and a sequence of commits that led to that snapshot (or more correctly, that it doesn't make sense to think of a commit without thinking about its pointer to the parent commit). That seems weird first, but everyone who understands how git works has internalized that, whether they explicitly think about it or not. After you understand that, it becomes easy to see that both the "technically correct" point and the author's point are kind of equivalent ways of saying the same thing.

But without this understanding, being told "branches are named sequences of commits" is probably worse than being told "a branch is nothing but a ref". The second one is cryptic and will soon be forgotten, no harm done. The first one leads you into a false sense of understanding, and soon you'll see an operation that looks like deep magic: someone moves the branch ref and now suddenly the whole branch is a completely different sequence of commits.

The confusion experienced by many people is largely due to the fact that a lot of articles try to teach git in a way that gives a false sense of understanding without explaining how git really works, which is exactly what teaching "Branches are named sequences of commits" does.