In general, the workers are not given enough information to replicate the product. They are shown how to attach a specific sprocket to a widget. The tasks are kept so simple (nothing to do with pleasantness) that no one can learn how the whole device is created or suggest improvements. This model lends to people being replaced by robots because human capital is one of the most expensive parts of running a factory.
In the case of Toyota, it sounds like these are high skilled engineers who are watching, understanding and making improvements to how the robots behave.
While the article itself is good, the title feels like link bait to me because the engineer's job is not to replace the robot but to enhance the robot. The dynamic isn't human vs robot as in the first scenario, instead it is human & robot cooperating.
With these types of factories, I think we'll likely see a resurgence of factories in rich countries as the most expensive component of the factory shifts from human capital to transportation of completed goods.
[edited for grammer, sic]