I’m not sure those are vapor trails produced by the same physics that creates the vapor in over-wing low-pressure areas on a F-18, say, during high alpha maneuvers. The pressure-related vapor is extremely ephemeral and is present only in the exact location of the pressure reduction, certainly not extending much behind the aircraft. And I have a hard time believing the tips of those big props are going supersonic, as a 540 Lycoming might do in an airshow. Will check on the tip speed.
As far as you thinking that those big Pratt Whitney props cruising at 2700 RPM can't generate those kind of prop speeds, look at the length of the props. There you will find the speeds to well exceed that of the IO-540 Lycoming.