To be fair, my understanding is the "10 is the last version" idea came from a developer speaking in an unofficial capacity and the media ran with it. It may have never been true.
While that is technically true, Microsoft didn't really make any effort to correct the misunderstanding, despite it being a widely reported story in tech.
I suspect they had a legitimate faction that was going to say "rolling release" and so they let it go.
It was definitely an official capacity because it was a Microsoft conference, but his phrasing was more like "latest" even though he said last. I think they misspoke.