Apple doesn't have an exclusive on 5 nm; it's also being used by Kirin 9000, Snapdragon 875, some Exynos, and a future Dimensity SoC.

I'm not sure how to square that claim with this sort of article:

https://www.extremetech.com/computing/315186-apple-books-tsm...

Snapdragon 875 is 5nm, but on Samsung's process not TSMC's[1].

[1] https://www.techpowerup.com/272139/samsung-foundry-to-become...

Rumors. Qualcomm is using TMSC 5nm for the x60 this year to be used in products Q1 next year. Same rumors. Though Apple will be using X60 on iPhone 13, so maybe a relation?

I believe it's about the remaining fab capacity that was available at that time

The article is obviously wrong.

There's also Samsung 5 nm.