Disclaimer: I didn't watch the video, but my assessment was based on articles like this one ( https://www.minnpost.com/metro/2020/05/what-we-know-about-th... ):

    Video taken by a bystander, 
    now seen around the world, 
    shows a police officer 
    kneeling on Floyd’s neck 
    for approximately five 
    minutes as he struggles, 
    telling officers he can’t
    breathe.

My thinking is that if you can speak for "approximately five minutes" while being strangled, then whatever you subsequently die of is not asphyxiation. I'm certainly open to being corrected on that, but yeah... it's not as if it matters.