It's not unusual for people to busy their hands and fiddle with things absently. For reasons I don't fully understand, it actually helps focus the mind. Baseball players are an extreme example of exploiting the focusing power of a seeming distraction, which explains why they're engaged in the unsavory habits of spitting tobacco juice, sunflower seed hulls, or gnashing gum like they're chewing cud when they're at the plate.
DD and I both utilize this in nondestructive/nondisgusting ways. An infant/toddler DD who didn't have a toy in her hand was a troublesome DD, so we always kept toys near at hand to offer. Pictures of her in that stage with empty hands are nearly nonexistent. She was usually not playing with the toy, but she had to have it in her hands.
So, I would not treat this as a behavior to be eliminated, but rather a behavior to be modified or channeled in ways that are non-destructive. If I saw him destroying something, I'd call his attention to it, make him clean up any mess he has made, and then suggest an alternative fiddling activity.
