I also read somewhere that it was a ruptured spleen.
I do recall that, maybe 2-3 years ago I speculated that the least safe aspect of our game was the punishment tackle that a diving player suffers as they touch down for a try. It is NEVER punished. Regularly you see the 'tackler' going knees first in to a player's back, or attempt to rip their head off, when the try was already done and dusted. For me, such tackles, needless, needlessly violent, should convert the already scored try to a penalty try and be accompanied by a red card. I have little doubt this was just the outcome I predicted at the time (that someone will get killed), only after which the RFU will wring its hands and then take 5 years to decide to 'do something'. It is the reason that American Football changed a touchdown to simply getting over the line with the ball, because they were having this exact same problem, what, maybe 100 years ago?
Was this the case in this tragic case? According to a friend who was there, yes. I suspect mobile phone and other footage will eventually emerge, but I am not sure that it would be the right thing to release, as his family have suffered enough already. However, there will have to be an inquest, and I guess a fuller story will emerge then.