Manufacturers had firmware that detected if the vehicle was in a test chamber (front axis moving but no G forces), if that was true then engine management would enable full emissions control and limit engine performance. If that was false the emissions control would be dropped and you would have all the horse power and acceleration that customers so dearly love.
I will say it explicitly: Whenever you see in the media the discussion on 'defeat devices', what it means is that manufacturers performed large scale fraud, _by_design_. I think people really fail to appreciate how severe this was.
The 'discrepancy' they discuss in the press release you link is just a euphemism to say, we don't want to go bankrupt and disrupt German GDP but we can't sell a car that complies with emissions regulation (i.e. not killing people ahead of time with air pollution) without making it have the engine performance/acceleration of a dead mouse.
If you take "partially fail of regulation" to mean stuff like "a defeat device switching emissions controls off if more than two wheels are spinning is not legally a defeat device", then sure. Otherwise, there are of course issues with testing methodology. At the same time, pretty much the entire car industry used defeat devices on their diesel cars.
