According to KBA, if the affected cars measured a steering input of 15 degrees or more, they would emit excess nitrogen oxide emissions. It's important to note that this is different than Volkswagen diesel CO2 emissions. The cars broke European strict emissions standards, so it's unclear what impact this has on cars in the US. Audi has recalled the A7 and A8, though it's unclear which Porsche models the KBA is investigating.
Fifteen degrees is a small amount of steering input. The wheel can move that much just to move around a pothole or bump in the road. Essentially, if you're driving, you're moving the wheel at least 15 degrees in one direction or the other.
If these allegations turn out to be true, it's going to be another blow to Volkswagen, Audi, and Porsche. While public trust in Volkswagen is supremely low, for the most part, Porsche's image has remained fairly clean. NOx emissions don't have as big of a long-term effect as CO2, though they're still bad for humans.