Nothing has changed in the airline assignment logic.
Since the first release, the ULD/Cargo containers are not supposed to be the same livery of the operator selected for the parking. They are, by default, related to the atc_parking_code of your own plane, in order to prevent funny situation of cargo with a livery on arrival different from the one on departure. Of course, if there's no atc_parking_code in the aircraft.cfg of the plane you are flying, the livery of the ULDs will be one of the airport operators.
And the small van is pulling the cargo crates?
That's because you haven't loaded the plane, so it results very light, calling for a small van and a limited number of carts.