If this was a courtroom and liability was being awarded, I'd blame Kupp 70% and Goff 30%.
It would have been a big time catch, but it was doable.
The throw could have been a tad better......perhaps. But the window was tight. It is possible that the ball was thrown the only place it could be because it had to be there to avoid defenders' hands.
In the end, I really don't find fault with either player. It was a tough position to be in, against a great defense, and in a small area to defend. It's not like Kupp was wide open and all Goff had to do was lob it to him.