Ruhl had what can be called "thick skin" in certain areas, areas that just won't come in no matter what, like Nasser's or Warren's backs. It's not water either, as he no doubt had pulled at least 20lbs of water with a loop diuretic. So what you see is a severely dehydrated guy at extremely low bodyfat with certain areas with "thicker skin" genetically.
If someone was holding water you'd see it in the lower legs, but Ruhl's calves were just saran-wrapped.
Someone like Phil Heath might not be thought of as grainy but he was always extremely low bodyfat and dry. He has what I call play-doh GH muscle. It look like slapped on very artificial tissue. Flex Lewis and Cutler had this look too. It's also genetic though the drugs, especially GH, don't help.