Did you PM the creator of the cake and ask him/her?
It gets fuzzy when I scroll in but it looks like a piece of green fondant that has been lightly spread with green frosting and they pressed a spatula and lifted it up all over it to "fluff" up the grass. I agree with the above, pm the originator. Happy caking!
Yeah I sent a pm last week but I've not heard anything back.
I'll have a try with some frosting this weekend and see what I can come up with.
There is gun for fondant with 16 disks. One of them makes grass. I don't know if this is made with that gun, but hope it helps anyway...
Wilton have a nozzle (233) which has little holes which can be used to make a grass effect similar to that one. You could use with buttercream or royal icing (if you look at my pictures I used it to create grass on the tent cake I did).