Many moons ago, when telnet chats were still a thing, one that I frequented had a guy turn up who was a BNSF dispatcher who found he could log in through the system and used it mostly to chat with his wife while not busy with railroad stuff.
I recall asking him about having someone to protect when a train backs up and he acted like he had no idea what I was talking about; he basically said if the train is coming people have to get out of it's way at crossings and the like. This kind of situation, a clearance issue, never occurred to me to ask. Apparently under their operating rules, a man on the rear of a backup move was not required.
So the bottom line is different railroads have different rules for rear end protection on back-up moves. IC may not require a man on the rear, particularly if they know the track they're using is clear of other trains. Somewhere someone dropped the ball on the clearance at this bridge.
Oh, and eventually the BNSF guy got busted, and we only heard from him like once more when he was at home.