None of the 10 announcers or commentators during the game mentioned anything about the hit being particularly via viscous or brutal. Instead they all said they had never seen anything like this before.
I am not any kind of medical professional. But if I had to guess, it would be Marfan’s syndrome, which, iirc, is a genetic weakening of the artery walls. Other athletes in the past have died rather quickly and unexpectedly from it, eg, Hank Gathers, Flo Hyman.