Bitter over Borrowed Burn

You are a floor judge of a Standard PPTQ. During a deck check, you find that Andy has some other cards in his deck box with the sideboard that are not on his decklist. You find 4 Magma Spray in blue sleeves. Arnold is playing a Mono-red deck in green sleeves.

After investigating, you find out those are cards he had lent a friend that has dropped and returned them, and you exclude Cheating. What do you do?

Andy receives a Game Loss for Deck Problem. Andy has extra cards with his sideboard that aren’t on his decklist. Since this was discovered by a judge during a deck check, the penalty is upgraded to a Game Loss.

Judges feel free to answer on Judge Apps!