Today i went to a restaurant that accepted bitcoin. When it came to paying, i scanned the QR-Code from the waiter with my coinbase app via the "sending bitcoin" button on the top right. I typed in the amount in Euro, scanned the QR-Code and hit send. The waiter then said that he didn't receive any bitcoin yet (this was maybe 20 seconds after i hit send) and asked if i did everything correctly. After i told him that i had used the coinbase app, he said that it doesn't work from an exchange and that the bitcoin I sent will be send back automatically. He said it would only work if I used my own wallet (e.g. via the "Blockchain Wallet."-App). I then payed in cash and left. 4 hours later, i haven't received anything back. So I checked the the transactions from the bitcoin adress to which i sent my bitcoin on blockcypher. Apparently, the bitcoin have really been sent back, however the adress (from which the bitcoin were sent and sent back to) isn't mine. The amount is the same and the time is correct, but if i hit the button with the QR-Code in the Coinbase app which shows a QR-Code with my adress, it's a different one.
Why is that, and how do I get my bitcoin?
Secondly, the waiter said that normally, the transaction would be done in a few seconds, if I for example used the wallet from the "Blockchain Wallet."-App. How would that be possible, wouldn't the transaction have to be verifyed be miners, nonetheless?
And thirdly, why didn't it work when i tried to deposit the bitcoin from coinbase to his address?
Sorry if these are noob questions