These miniatures had a very high rate of spawning from lunar fortunes at the beginning of the event due to a coding error. They now have a much less chance of spawning from fortunes, but they are easily gained from the Celestial Pig.
During the event these items saw an extreme change in the price people were trading them for. Initially the price started relatively high and then plummeted when people found out they were awarded in the final event, making them very common.
Chinese Folklore designates 2007 as the year of the Golden Pig, an event that happens once every 600 years or so. The Folklore surrounding the Golden Pig is minimal, and mainly stems from a Korean story from the Silla Kingdom (57 B.C. - A.D. 935) in which a Magistrates wife is kidnapped by a magical Golden Pig, rescued, and later gives birth to a son she believes is the child of the Golden Pig. The Folklore surrounding this calendar year is likely why the miniature pet's item lettering is gold while the item itself is common.