I'd argue it doesn't show growth or shrinking. What capacity does remembering strings of numbers "grow"? There's no clear connection to remembering other things

I'd argue it doesn't show growth or shrinking. What capacity does remembering strings of numbers "grow"? There's no clear connection to remembering other things, or math skills, or anything but how many numbers you remember. The author says they still remember these numbers. Maybe they remember fewer and this is shrinking? Seems like a poor example at any rate.