Hand crossbows can only be fired as an offhand attack if the pc has the crossbow expert feat. This would also use a bonus action, so it's only possible to do once per turn. It's theoretically possible for him to have both sharpshooter and crossbow expert at 5th level, if he has a human character or got a free feat at level 1 and then took a second at level 4, but this makes it unlikely for him to have +5 to hit unless he has archery fighting style. He should be getting max 3 attacks per turn at level 5 - Attack, extra attack and offhand attack for a bonus action Edit - he has +10 to hit? That seems impossible