Nothing I’ve seen yet suggests that the items were stolen from any rightful owner. Only that they were “mislabeled” on a customs form. It doesn’t strike me as mislabeling if they were described as “tiles”. They’re clay. They’re fired and hardened. Would “tablets” be better? But they’re not whole tablets. They’re fragments. They’re... Tiles.
There’s a lot of explanatory stuff at the article link.
Sounds like they are broken tiles.