Yes, the sound your hear is the air pipe breaking and thus the full emergency brake application being applied. As was alluded to, while the brakes on the entire train are applied, one must consider that the entire trailing consist still on the rail, while the brakes are applied, is much heavier than the 2 or 3 locomotives in the consist (I've not found the report, but I believe I was told there were 2 locomotives on the train). As such, basic inertia comes into play and thus the brakes are able to bring the locomotives to a stop much faster than the trailing cars.
As the crew was probably hunkered down under their control stands, they probably weren't thinking about overriding the emergency brake application to move forward and clear of the oncoming rear portion of the train.
The US is currently moving to electronic braking systems to suppliment the air brakes. This system uses a wire running parallel to the air hoses that allows for faster activation of the brakes in both normal and emergency situations by electrically actuating the brake valve on each car individually (and thus simultaneously) instead of relying on the air reduction of the main pipe (which travels at approx. 2000 feet per second if I remember correctly) to cause the application.
