When a definition explains everything, it explains nothing. So he goes on to setup some boundaries and describe some narrower qualities to try and help us reason about the nature of those things.
The only similarity between your keyboard and an AI agent is that they both have utility. You might say: "I used AI to write my essay" or "I used my keyboard to write my essay". It's very deceptive and easy to get trapped in thinking, these are the same, in both cases you just used a tool to write an essay with? AI is just a tool, like a keyboard. What Rich is trying to bring about is that there's actually a world of difference here. And if you keep thinking of a AI as "just a tool", you're missing that entire world of difference. It becomes much better to think of AI as automation and leave the tool definition to the keyboard. Now instead of saying "I used AI to write my essay" say "I automated the writing of my essay, I did not write the essay, AI did". That latter framing is so much more accurate, and changing that framing and perspective is going to give you a much deeper understanding of the impact, trade-offs, consequences, etc.
It's less about code structure, maintainability, readability, algos, class/function abstractions, etc.
And to Rich's point, you're not getting to experience the process of coding anymore, what you'd have learned by doing it, about the domain, about logic, about structure, you're missing on that. You're likely learning something else though, at a higher plane, and maybe about managing autonomous agents, and so on.