I agree with your sentiment in general: we should not make assumptions about the parameters of others' relationships.

But in this case, Huang himself explicitly mentioned the hurt that he caused his family. I don't think it gets much clearer than this.

    I owe my family and all of you an apology.

    I was unfaithful to my wife. My actions hurt her and 
    our children. There is no excuse for what I did. I am 
    deeply sorry.

    Throughout my life, my family has given me love and 
    support. They deserve my honesty and loyalty. Instead, 
    I let them down and damaged the life we built together. 
    I take full responsibility for what I did and the hurt I 
    caused, and I accept the criticism that comes with it.

    To my wife and family: I love you. I know an apology 
    cannot undo what I have done. I hope our family will heal 
    and that, over time, I can earn back your trust.

He wrote himself a press release saying he was unfaithful and because of his actions he hurt his family... it sounds pretty clear that was not a consensual non-monogamous relationship. https://nvidianews.nvidia.com/news/a-message-to-our-company

If it was an open marriage, why would his first statement have been an apology to his wife and family? I don't see any reason to start assuming it was actually fine. In any case the affair becoming public in such a way would still be hurting them - the media attention you're speaking about. Much worse than a divorce, right?

he wouldn't have publicly apologized if all of that was "perfectly fine" with his wife

Might wanna google the term “affair”

He publicly stated he broke his wife’s trust, buddy.

People don't need facts when they just want an excuse to attack someone from the outgroup.