It doens't take into account the mental labour of actually assigning each card a numeric alpha address.
I appreciate that he takes a moment to acknowledge that this step of assigning numbers and arranging is work. Many gloss over this.
The work put in up front ideally pays off later.
"Personal knowledge management is an aid to your work, not the work itself." —Sam Matla #
This is entirely dependent on what and how you're doing it. If you're actively reading and annotating, and placing it somewhere, then that is the work, just in small progressive steps.
He needs to be more specific about what he means by "personal knowledge management" as a definition of something.