The choice to make it out of miscellaneous parts rather than the 1x1 round plates or 1x1 round tiles found in most mosaic sets makes it look like Lego just wanted to get rid of the parts that they had sitting in surplus. Even shaping the details with wedge plates such as in The Rolling Stones (31206) set, or a mix of 1x1 rounds and wedge plates such as in Hokusai – The Great Wave (31208), would look much nicer and less slapdash.