Thank you.

Based on canon, the Stone was being removed from the care of Griphook's organization at that time. It seems less likely he'd be concerned about theft and more likely he'd be concerned about what impact the Stone might have on his people.

It's still a stab in the dark. But since pretty much the only thing we know about MoR!goblins is that they run 'banks' and they are in a constant state of war with counterfeiters, I think it's the best guess possible without diving out of MoR and into canon even more.