That is absolutely true! That's why its been published all over the place to disconnect the rear driveshaft when towing a toyota truck, regardless of whether its manual or automatic.
If its been towed for a good portion of its life (hence, the 500k on the odo), its possible that the transmission will need work. Toyotas are strong vehicles, but that's a ton of miles to put on it without any moving lubrication while towing.