Having read some of the underlying documentation, this appears to be an "undeclared AECD" issue as opposed to an "intentional cheat" issue.
To illustrate the difference:
VW: "If vehicle is being operated on a dyno, use emission strategy A. Otherwise, use emission strategy B." That's not legal.
Chrysler (example, because I don't know the exact circumstances): "If vehicle speed and load conditions exceed X, ramp down EGR." It so happens that X is never exceeded during the test procedures ... but if they did, it would work the same on the dyno as it did on the road. This, as I understand it, is quasi-legal and can be approved by the authorities (therefore legal) IF the strategy is declared as an AECD - but they didn't do that.
All engine manufacturers "teach to the test" and calibrate their systems (not just emissions) to pass the tests that they will be subjected to. What happens when conditions are present which are outside of those experienced in the test ... varies.
Spark-ignition gasoline engines typically run richer than stoichiometric (no longer in closed-loop operation) when you mash the accelerator all the way to the floor, for example. That creates enormously more HC, CO, and PM than the regulations otherwise allow. But it's approved as an AECD (and has to be declared and approved!) because the consequence otherwise would be melted pistons and exhaust valves and it could destroy the catalyst.