The USPS sends two - one to your old address and one to your new address. The one sent to your old address does indicate that they’re redirecting - that is, it

The USPS sends two - one to your old address and one to your new address. The one sent to your old address does indicate that they’re redirecting - that is, it is sent after the fact, it is not asking for confirmation or providing a grace period before they do - but it is marked clearly as something that should not be forwarded. I suppose it could have been forwarded by accident (at scale screw ups do happen), but perhaps you confused one with the other?