This important measurement was made using Cassini's INMS instrument, which detects gases with the goal of determining their composition. INMS was designed to sample the upper atmosphere of Saturn's large, smoggy moon Titan. However, after Cassini's surprising discovery of a tall plume if icy spray erupting from cracks on Enceladus in 2005, planetary scientists turned its detectors to that small moon.
Furthermore, the icy stuff that collected on Methone's surface could even be more lightweight than that which lies beneath. It is possible that such fluffy, snowy, stuff can actually flow--at least over long periods of thousands to millions of years--thus filling in the tell-tale scars of impact craters.
Conventionalized images of the Man in the Moon seen in Western art usually display a simple "face" in the full Moon, or a human profile in the crescent Moon, that correspond to real topological features on the lunar surface.