A Jagex Moderator has confirmed that this was a joke added by the Content Development team, as quoted below:
...Content Development often add little jokes to their updates. Sometimes we're told about them before they're added to the game. Occasionally, they believe that it would be more amusing to just add them without telling us. Then we get lots of messages asking what a 'Thingy' is...
As mentioned above, this item is completely unobtainable and has since been removed from the Grand Exchange. If you attempt to look up "Thingy," nothing will appear to match the search.