He says strictly speaking, legally you're not allowed to reverse a train once passengers are inside without permission, but you can "rock" the locomotive forwards & backwards if you're stuck.
Procedures may differ in the USA.
Think of trying to keep a rope straight by pulling on it, vs trying to keep a rope straight by pushing on it.
The passenger train rule is because its hard to kill people by tipping over coal cars especially when its a rare failure mode anyway. But you wouldn't risk it with cars full of passengers.
(Oh and edited to add WRT switches, its subjectively 10 to 100 times harder to derail on a switch going one direction than the other, so again you'd risk backing a bunch of coal cars thru a switch but it would be pretty dumb to do it with cars full of passengers)