There is a difference between the "contrail" of an F18 taking off or an F16 making a sharp turn. These contrails are formed because of a local higher air pressure due to the manouvring which compresses the air.
The contrails left by airliners/fighters enroute is indeed because of the vaporized water/fluid coming out of the engine at colder tempratures. The lowest I have seen them was on a clear over Germany at FL240, near Ramstein airbase when a 737 passed underneath us. Spoiling some of the nice surroundings.