Not defending VW or saying this POV isn't plausible.
But many in the management old guard are still shockingly technically illiterate, most of my generation just get by at best. It's not impossible the manager wouldn't have a clue about the nuts and bolts of what the engineers did unless someone told them, they'd never find it on their own. Nor is it impossible the managers essentially told the engineers 'I don't care how, just give us the results we want/need.' Just another plausible scenario.
I doubt most employees even today, young or old, know enough to question much in the IT realm - they have to 'trust Hans & Franz'
Anything is possible, and there is something to what you say. However...
from what I'm reading, VW managed to pass the US emissions test with less hardware than their competitors, and still get good performance. Maybe the very top level would not be asking questions, though I suspect that a corp like VW has a Chief Technology Officer - our megacorp did, and he was definitely a technical guy - and it would be his job to understand the technical reasons that VW could achieve this (and patent it?).
As I described earlier, it could have been a very small group that actually wrote the cheat code and inserted it as part of the last integration step (so no one else saw it). And the cheat code likely just took advantage of existing variables/flags that normally existed in the emission control software modules for other valid uses (testing, debug, evaluation, QC, etc), so no suspicion would be raised at that level.
But I just can't see a scenario where two engineers in the module integration ('packaging') team would be motivated to do this. 'Packaging' is not a glamorous, sought-after position, it's a thankless, nuts-and-bolts sort of job. Those engineers would not be rewarded (internally) for getting the emissions down, no one would even look to them for that (which is why it would be a good place to insert the cheat code).
Far more likely that it was driven by someone with management authority (lower than C-level maybe). Someone who could manage to get some trusted, paid-off 'ringers' onto the packaging team to pull this off. And someone who would really benefit with bonuses/promotion for getting the cars to pass the test.
I'll be shocked if this comes down to a few low-level engineers working independently from management (unless VW does a really good job of hiding the evidence, and throwing some engineers under the bus). Follow the money - they just wouldn't have the incentive, and probably would have been caught if it weren't for some collusion.
-ERD50