>>97576892He means that people have been able to watch it for 3 years. It also is the start of her DMC3 playthrough. People often watch the start of playthroughs, thus boosting views.
Also, probably not in his point, this would have been 2021-22, around when CouncilRyS debuted. That was when Vtubing was still decently young in the west. That isn't going to work as well when there are around 100 lolis running around, and hundreds of thousands to millions of vods to watch. Not saying that Gura wouldn't be popular today, but not 4.5 million subscribers popular.