Not sure if its a ping pong ball or not...
http://www.marcospecialties.com/pinball-parts/31-2816.1
*Edit*
Did a quick search on the specs of a ping pong ball and found this:
"International rules state the ball shall weigh 2.7 grams and be 40 millimeters in diameter."
Marco ball weighs 3oz so I would say its not a ping pong ball.. definitely heavier.