In the video, it’s framed that the world thinks manga is a “uniquely Japanese” thing but the video counters that by using Eike Exner’s book on manga history.

I didn’t finish the video yet (this is just the first minute or two) but I am going to guess that it’s either the Meiji period or the American occupation having influence on how manga eventually developed to what we know today. This is the same argument used by theorists like Azuma Hiroki but he talks about otaku culture more broadly.