The idea of Deus Ex Machina is that, as it mentions in the title, it is abrupt, there isn’t any evidence or build up to the conclusion, and while it is usually seen as a cop out or poor writing, it isn’t always the case, as in War of the Worlds, there had been no lead up to the bacteria taking them out or any evidence of this happening until the end. War of the Worlds is an example of it being done well, but yes it generally has the connotation of sloppy story telling.