But what the video explains is the fact that the rounding is actually less fundamental than the length of the resonating tract. It means that you can keep your lips unrounded and produce a vowel very, very similar to the canonical /y/
Edit: I made a typo in my original comment, I meant to say "by centralizing /i/ slightly" (not "/u/")
What is this supposed to mean? It isn't possible to maintain a phonemic distinction between sounds that aren't phonetically distinct.
FWIW I'm even not sure there are any languages that actually have a phonemic distinction between /y/ and /ʉ/ or between /ɨ/ and /ɯ/. I'm sure there are some, but I would be very surprised if the actual distinction cannot be more sensibly analyzed in other terms (length etc).
https://en.wikipedia.org/wiki/Norwegian_phonology#/media/Fil...
In the phonetic realization section, though, there's this:
"The close /ʏ, yː, ʉ, ʉː/ have been variously described as protruded [ʏʷ, yʷː] and compressed [ʉ͍, ʉ͍ː] as well as compressed [ʏ͍, y͍ː] and protruded [ʉʷ, ʉʷː]. The backness of /ʉ, ʉː/ has also been variously described as central [ʉ, ʉː] and near-front [ʉ̟, ʉ̟ː]. Therefore, /ʏ, yː/ may be differentiated from /ʉ, ʉː/ by backness and the type of rounding or even only by the type of rounding"
This last bit is actually even more surprising: two front-ish rounded vowels that are distinguished solely by how the lips are rounded? I can't help but wonder how stable such an arrangement could be long term.
> Rounded vowels have two types of rounding: /ɵ/, /ʉː/, /ʊ/ and /uː/ are compressed [...] > /ʏ/, /yː/, /œ/ and its pre-/r/ allophone [œ̞], /øː/ and its pre-/r/ allophone [œ̞ː], /ɔ/ and /oː/ are protruded [...] > Type of rounding is the primary way of distinguishing /ʉː, ɵ/ from /yː, œ/, especially in Central Standard Swedish.
https://en.m.wikipedia.org/wiki/Swedish_phonology
More about different kinds of rounding at https://en.m.wikipedia.org/wiki/Roundedness