It was either Dark Energon or an AllSpark shard that brought the trucks to life
Either can make Earth machines act crazy and aggressive. Energon brought the Cybertronians to life, so maybe it could animate terrestrial machines too.- An AllSpark shard gave life to the helicopter that saved the survivors.
The helicopter at the end of the movie wasn't going to save the protagonists
Think about it. In the original short story, the narrator mentions the possibility of the trucks enslaving humans and using them to make more of themselves (which they would need in order to take over the world, given their lack of hands). He then looks up at the sky and sees two airplanes flying overhead and says "I wish I could believe there are people in them."Presumably, then, the voice recording inside the helicopter was a lie, and it was actually kidnapping the main characters and taking them to a prison/factory where they will be enslaved by the vehicles.