G'day Steph,
lol, What a question!! The seeds of the Quandong tree are round, pale and knobbly, early settlers used these for making necklace beads, stud buttons and Chinese checker marbles, also for medicinal purposes. Today, they are only rarely used for these purposes, by locals and art and craft shops. So I would say no to that Steph, they would be no way classified as marbles here.
Tome.