Thanks for the link. Addicted to this game currently!
The noise they are referring to is probably a perlin noise texture that is used to determine which of two textures to sample from in the pixel shader. If you look at the grass closely it looks "randomly patchy". So it's likely two textures, and a third texture (the perlin noise) is used to determine how much from each of the two source textures is used in the final output. This is usually referred to as multitexturing.
The soft filtering, I'm guessing, refers to the smooth transition from grass to dirt (or whatever) along the tile edges. This is yet another level of multi-texturing, probably using another "mask" texture that has different "shapes" in it for the different neighbouring patterns of tiles (instead of the noise texture).
I know about perlin noise, it used to create natural thing like cloudy, grass, fire... even generate random Map. So i think it has nothing to do with smooth.
About the smooth transitions between tiles, It's about blending , and there are tons of artile about it, so I thinks it's not very hard. After working with smooth edge, I'll move to the blending issue. I think it will be alot easier than softing this edge.
Anyway, I'm still not sure this is the best approach, I think there will be a better (in performance, or visual quality). So if any one can enlight me, I will really appreciate it. I will post anything that I found here.