By the rulebook, when the air dumps on a train you're supposed to make an emergency broadcast, because 70 cars back you could have spilled stuff all over a parallel main track. Now, in practice this is rarely done, the air can dump for a variety of reasons, and if pressure comes back up, there isn't a break in the brakepipe and you're good to go. But this is exactly what happened here... seeing the passing train coming as the air dumped, the grain crew should have been more aware and made that emergency broadcast...