I would not use dismount from a helicopter. I would use it for a horse. I it's OK for a motorcycle. With internet news sites, things are often published with sloppy language usage. I have no idea whether this is the case or whether the author of the article would normally use that phrase/ It could also be the case that the author felt it applied to the way the person got out of the helicopter on that occasion- maybe they jumped out the second it hit the ground.
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