That's odd SOA would say no hitch given that towing capacities are listed for other markets for the same vehicle.
The Subaru Australia lists the "New" Impreza towing capacity 650 kg to 1,200 kg.
The Subaru UK site and the XV towing capacity is listed as 1,200 kg to 1,600 kg. They don't have the new Impreza specs up yet. But the XV is essentially the Impreza. At least from what I have read.