Camshafts are usually made out of steel. They have to be extremely robust because they do not have hydrodynamic lubrication. The camshaft only spins at half the engine RPM, but it is subjected to much more friction than the pistons. Similar to the crankshaft, the camshafts require a girdle that locates them.
If Honda made this more compact, then it stands to reason the cams are thinner, and the girdle is closer to the valve tappets/rockers.
However I don't think he's merely talking about the camshafts, rather the cylinder heads. This means globally the engine has shrunk. Skeleton meaning all the fat has been trimmed away. In fact it only burns fat now