Kevin seems like the kind of jerk to have flown out the previous night - he's a bird, that kind of flying - found and emptied the chest, covered his tracks and then flown back before being noticed.
Detecting pre-disturbed sand is a lot harder than doing the same for dirt. The bear might not have been able to tell.
And I bet Kevin had the bear pay for his plane ticket over there. I mean he can fly, but probably not that far. Ideal sob story.