In the event of it actually being a scam, that would be the most idiotic scam ever and that guy would be fired in no time.
It's much more likely he typed the numbers in to check the balance. When people steal money this way, they have to know exactly how much is on the gift card. If you have a $75 card and the bill is $80, you're going to notice right away. This is usually only done with partial cards so that they can take $5-15 on a large bill without anyone noticing. $30 on an $80 is insane and it's no wonder he was caught.
But the most telling aspect is that when confronted he didn't check the card or apologize. If I'm accused of something like that the first thing I'm going to do is run the card to see if the amount was taken out anyways, despite not being on the receipt. You have to make sure the customer didn't just lose money due to some malfunction.
If he looked at the receipt he didn't need to look at the card. Then again. Olivia didn't say he looked at it either. ---