I'll also note that Daniel has for some time not been a Debian Developer (there was some drama there, the details of which I wouldn't want to recall even if I remembered), and "Debian Live" has been not an official Debian project for a while -- it's running on live.debian.net (not .org), it's running on servers personally run by Daniel (not by the Debian sysadmin team), etc.
That said, IMO the distinction of "not an official Debian project" is less about where the service is running (it's a volunteer project, anyway) than about how integrated it is with the rest of Debian. For a while, Debian Live has been showing strong signs of being Daniel's personal project -- with a lot of users, to be fair -- and not really working with other Debian teams or developers. I think that's what came to a head here.
It's been a while since I worked on this, but IIRC Ubuntu's live image is based on Casper, which is a separate system from live-build (though live-build supports using Casper).
Also, bear in mind that the specific reason this happened was that there were features live-build didn't support, like UEFI boot, that the Debian project needed. This entire kerfuffle came about because Debian wanted a better live boot system.