https://www.records.nsw.gov.au/sites/default/files/GRR/Storageboxes-2018.pdf

https://www.records.nsw.gov.au/records-repository/storage-boxes

I just gonna throw this out there. If these are standard government document boxes (see the links above). And you do the Math based on a stack of 6 boxes, that comes out to just about 5 feet tall stacked on a Pallet. A Truck is a touch over 8 feet tall inside. So based on just scale I would say those could be document boxes. Also it could be a climate controlled truck, not sure because the pic is bad but there is something dark on the rear wall that looks like a reffer unit. See bellow for diagram.

https://boxart.com/transport/truck_20ft/