I believe they’re talking about the process where your landscape texture/mask propagates it’s diffuse value to the foliage above it, I remember trying to follow something similar when I was at university, but struggling to get it to work.
Generally the aim is to make your grass match the colour of the landscape below it. The first thing I notice about your image was your grass “pops”, it’s too dark and the scaling is way off.
First I would match your grass with the colour of the terrain, then work on your scaling, the grass blades are way too large for the size of the hills e.t.c - put a character from the UE4 content files for reference.
Your terrains specular/roughness seems odd from a distance - are you using normal/roughness maps? the hills look too smooth & shiny.
Also try adding exponential height fog to help grey out the terrain at the distance, this emulates atmospheric perspective - where distance terrain/objects decrease in saturation and take on the colour of the atmospheric haze.
And as said above, using techniques to break up texture tiling helps a lot!.