Wow, I have never see this grass that act like a waterbed and it is a small mound. It match with the turf outside of the mound. I don't know if the rain fill it up underground of where the mound is to rise up and act like a waterbed type.
As for Jiro, I don't think the mound has nothing to do with the turf type of grasses. It is like science, found a way to make the grass soft and act like there must be water underneath. This is the first time I have ever see this. Very rare to me. It is remarkable. I am flabbergast. Wow. Incredible.