procedural generation – FMB change based on derivative and noise value

I'm still working on my procedural terrain generation and the ideas of Sean Murray (No Mans Sky programmer). I looked at this GDC17 presentation, but there are a few things that make no sense to me:

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Change the amplitude based on currentGain AND noise value? This leaves only all highs (large noise values ‚Äč‚Äčlike 1) unchanged and the small ones make the amplitude really tiny. How does that represent the height erosion?

The audio also does not help much, he did not go into code details.

Any ideas that make sense?