‘Going to the ground’ becomes a very grey area when the Receiver/interceptor goes out of bounds. What if he landed on the Bills Coach that was right by him? What if a Bills player on bench held him up and prevented him going to the ground? What if an opposing team player on sidelines didn’t get out of Poyer’s way?
The reason it was ruled an interception on the field is because he went to the ground so far out of bounds the refs didn’t see the bobble.