There is a camera pointing forward in all railroad locomotives.
The Train Came "Out of Nowhere."
The best graphic of the site came out in the Wall Street Journal and a clue was provided by a railroad employee posting on Trainorders.com. As the U.S. calendar advances from the fall equinox to the winter solstice, the sun sets in the west southwestern sky.
That Midland Crossing is in a "Quiet Zone"
In most parts of the country when a train approaches a crossing the crew sounds the horn with two long, one short, and one long blast. According to the article at the link, the crossing is in a "quiet zone" where the crew does not routinely sound the horn. It is very likely the horn was being sounded as the train approached the float but it is possible the horn wasn't sounded as early as it might have been if the quiet zone did not exist. This may have added to the perception the train "came out of nowhere."
The Railroad Crossing Activation by the Approaching Train
This is not up to the railroad. There are federal requirements for the timing of the lights and crossing gates.
Addition: Updated timeline from the Los Angeles Times.