A common procedure was to have the lead bomber(s) (with the best trained bombardiers and the best bombsights) identify the specific target and drop mainly incendiaries on it – then the following planes aim at the fires from those, and drop their loads of bombs on them. That is probably what they meant by “release on his command”. It’s not every plane actually dropping their bombs at the same time, but every plain aiming at the same point (as marked by the flight leader).
And actually, damaging the hospital and civilian (housing) areas beyond is probably also effective in reducing the productivity of the factory. Most of the workers tend to live nearby; destroying their housing (and possibly killing or injuring them/their families) will reduce productivity. Not as much as a direct hit on the factory, but such direct hits were really very rare.
Of course, there are moral questions if they were to deliberately aim at civilians.