How did sword end up by the lake when goblin stole it in Gryngrotts Harry Potter 7?

In Harry Potter and the Deathly Hallows, it was actually Ron, not a goblin, who was tricked into taking the sword that the goblin Griphook had stashed by a lake. The goblin did later try to steal the sword at Shell Cottage from Ron, after Harry, Ron, and Hermoine escaped.