Apple did say PCIe Gen 6 - in the original version of the press release. That's where the quote came from. But they have now changed it to exclude the reference to Gen 6:

"Storage performance is up to twice as fast, with a next-generation SSD architecture, delivering industry-leading read and write speeds for rapid project loading, file transfers, and loading huge LLMs."

Here's the original, archived press release from August 25th (look under "Blazing-Fast Storage and Pro Connectivity"):

https://web.archive.org/web/20260825130329/https://www.apple...

And here's the first modified version that the Wayback Machine has, from August 26th:

https://web.archive.org/web/20260826020313/https://www.apple...

So it seems like Apple made a mistake in this case. I agree with you that it will likely be PCIe Gen 5 - that's much more logical.