No need to worry. Beardies have a natural instinct to dig, regardless if there's anything to dig with.
I used to have a male beardie who loved (understatement) to dig. He'd clean out the sand that was in his tank to the point where you could see the bottom - not a grain left in that area. He'd also attempt to dig in cardboard boxes (though he never got anywhere :roll
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You could make him a sand box (with sifted play sand) either inside his viv or for when he's out to roam/play.