Just to show that windrunmer squires have gravitation, in part two of oathbringer, we hear
“Drehy, you used a quarter of a Basic Lashing, by Kaladin’s terminology?” Sigzil continued, still making notes.
A basic lashing is part of the gravitation surge. So it leads me to think that squires have gravitation. And therefore Rock could have used gravitation. I do still think it is weird that Brandon brings up how odd it is that he can draw the shard bow so it still might not be gravitation, but im still married to the idea that it is caused by some surge, possibly even tension (It would be slightly funny to have our first stoneward to be called Rock, I don't really think he would be a bondsmith but I have no basis for either possibility). Still I can't wait to read and find out, in the unfortunately maybe delayed until around book 5 novella for Rock.