> He slept with someone who worked directly under him, under what universe would he be allowed to stay at Nvidia?

Under these universes that haven't fully internalised the current American corporate morality. Which in itself is a very modern construct.

In many places and times 'sleeping with someone working under you' warranted at most a shrug.

Maybe in today's day and age, but sleeping with your boss who is married was never a normal or okay thing in any part of the world as far as I recall, maybe it changed in the last few decades, but I've never known anyone to think any of this is normal.