And they cheated.
Stellantis cars believed to have used defeat devices.
Citroen C4 1.6 BlueHDi believed to use thermal window and hot start cheat devices
Peugeot 5008 1.6 BlueHDi alleged to use defeat devices.
Vauxhall Mokka 1.6 CDTi believed to use thermal window and hot start cheat devices.
Vauxhall Insignia 2.0 CDTi alleged to use defeat devices.
Other manufactures beside VW suspected or known to use defeat devices are BMW, Dacia, Fiat, Hyundai, Honda, Jaguar, KIA, Mazda, Mercedes, Ford, Nissan, Range Rover, Renault, Suzuki, Toyota, Volvo and of course the one that actually got caught, Audi, VW, Seat, Skoda, Porsche.
Source Motoring Research.