The wiki is pretty comprehensive. Have you navigated to the bottom of the page for links to other tab options?
https://planetside.co.uk/wiki/index.php?title=Cloud_Layer_v2 (Yes I realize this is Cloud Layer v2, but it has most the bits and bobs. I'm not sure where v3 page is. I tried manually entering it into the URL and it redirected back to V2 clouds.)
What he has done is used the Final Density as the Density Shader. The Final Density is handy to add filler or haze between cloud shapes, but can also be used to mask, and other stuff.
When there is no Density Fractal plugged into the Cloud Layer, it creates a solid blanket of cloud at the desired albido settings in the Colour Tab. So he's basically just "Masked In" clouds, as apposed to using the Density Fractal to tell the cloud layer to create the clouds from noise.
One thing I would suggest is to give some testing a try. What if you plug that Final Density into the Density Fractal? How does it look than? Better, worse? What about with/without the Depth Modulator? (
https://planetside.co.uk/wiki/index.php?title=Cloud_Layer_v2_-_Functions_Tab)
From some quick testing, it seems using the Final Density creates smoother clouds with the Depth Modulator. Interestingly, quicker render too.