Sophia Ok, I'll bite. What is written there is complete gobbledegook. The piano is tuned, there is absolutely NO NEED for perfect pitch. In fact even singers don't need perfect pitch - that's what tuning forks are for.
What is that writer even trying to say????? NONE of the skills mentioned are needed as such. You don't need to be a composer to enjoy making gorgeous music. What is that book trying to teach???
The only thing I agree with is (somewhat) that you need to be able to hear what it should sound in order to produce the sound that is needed. But the rest, excuse my colourful language, is sheer BS.
I think the theme is mental practice. And I believe he's saying mental practice uses absolute pitch to help with the memorization process. Here's a link to the page with the below quote (I don't want to keep quoting too much since it's copyright material.): Learning Relative Pitch and Absolute Pitch (Sight Singing, Composing)
In that section* we saw that the final objective of memorizing is to be able to play the music in your mind (mental play, MP). It turns out that, by paying attention to RP and AP during the process of practicing MP, you naturally acquire the pitch skills! Thus, you do not only play music in your mind, but you must always play it at the correct pitch. This makes perfect sense because, without playing at the correct pitch, you lose so many of the benefits of MP. Conversely, MP will not work well unless it is done in AP, because MP is a memory function, and memory is associative and AP is one of the most important associations β AP is what gives music its true melodic lines, color, expression, etc.
*He's referring to the Memorizing section.