Like thinking he ordered X amount but it was actually Y amount, or placing an order and it taking so long you forgot about it so you place it again, or ordering

Like thinking he ordered X amount but it was actually Y amount, or placing an order and it taking so long you forgot about it so you place it again, or ordering the wrong product code and failing to verify it, or skimming over the order and missing that the salesman added extras for whatever reason and signing it anyway, or… If he didn’t remember placing the order, or believed that the order was modified, then at worst he’s mistaken, not lying.