The Verge asked a rep at Microsoft, and this is what they said:

When I reached out to Microsoft about Nixon's comments, the company didn't dismiss them at all. "Recent comments at Ignite about Windows 10 are reflective of the way Windows will be delivered as a service bringing new innovations and updates in an ongoing manner, with continuous value for our consumer and business customers," says a Microsoft spokesperson in a statement to The Verge. "We aren’t speaking to future branding at this time, but customers can be confident Windows 10 will remain up-to-date and power a variety of devices from PCs to phones to Surface Hub to HoloLens and Xbox. We look forward to a long future of Windows innovations."

So they didn't rule out branding changes, but the changes to Win 11 seem like a pretty big change from Win 10, which seems to go against the "Windows will be delivered as a service" statement. So it's not just that one engineer, but probably a broader push (that may have been delayed or scrapped) to push gradual updates consistently instead of larger, periodic updates. I'm no expert, but I didn't really see much difference in how Win 10 was released vs previous versions (e.g. XP, 7, and 10 all had service packs).

Wasn't the entire point of not using "Windows 9" branding and instead going straight to "Windows 10" from 8 that they didn't want the last version of Windows to be 9, that they preferred a nice round number.

frankly as long as my windows 10 license is valid in windows 11, i couldn't care less.

But you still wouldn't find me using windows 11.

well the way they stopped making new windows versions after 10 (until now) seems to indicate that was the plan