There is a second variant worth knowing since you may see it next: the money arrives, nobody contacts you at all, and weeks later it is quietly reversed.
That one is not aimed at you. It is somebody testing whether stolen account details work, or laundering through a chain of accounts. It looks harmless and it is why an unexplained credit is worth reporting even when nobody asks for anything.
The rule that covers both: an unexplained credit is a thing to report, not a thing to react to.