Transparency has nothing to do with it. If you look at the overall content of his YouTube channel, it's pretty clear that it only existed for the primary purpose of promoting GME. Almost every single video he posted within the past six months either had GME in the title or GME in the image representing each video (or both) which screams that he's on a soapbox with the GME thing. I'm sure every hedge fund manager out there would love the freedom to do what this guy has done, which is take a sizable position and then set up a YouTube channel dedicated to promoting the position to the masses. But they are not allowed to do that.
If he would have just taken the position privately and not constantly promoted it, there would be no problem. It's market manipulation because it involves exposing other people to the position through the channel and then persuading them why it's a good investment. Essentially what he's done is created a church around GME and designated himself as the pastor to all who will walk in and listen to him preach about it in the microphone. And for every GME believer that's created and buys the stock, it can only help out the pastor's position because he got in long ago.
The problem is that churches were designed for religions, not for equities.