Author here! It's very true that the GPU does the heavy lifting, although I'm not sure exactly where an "in the browser" line could be drawn (conceptually any page uses the browser as an execution engine and library).
It's a bit trickier due to restrictions in WebGL (OpenGL ES based) compared to the desktop (e.g. no bitwise operators makes it a pain to get randomness that doesn't bias the result), but it's basically the same.
It's a bit trickier due to restrictions in WebGL (OpenGL ES based) compared to the desktop (e.g. no bitwise operators makes it a pain to get randomness that doesn't bias the result), but it's basically the same.