That looks to me like actual mail. Doesn’t matter. What is shown here is still illegal where I come from. Carriers are required to keep their mail secured at ALL times. You cannot carry mail in an open situation like this is showing. If you leave your vehicle for any reason you are required to lock your mail inside the vehicle.
That said, the trays are used to carry your sorted mail and they are emptied as your mail is delivered. At the end of the day, you have a bunch of empty trays that are left inside the post office.
John see post 1,989. IF it is a carrier, If it is mail. (If we had more information available. Cameras along route?
This maybe something for the OIG USPS to investigate.