Confused on a Touchback Call

[Rick Vietti]

I was visiting Illinois last week and I had the chance to catch a playoff game from the town I used to live in. Below is the play and the resulting call. It did not seem right to me, but I have only officiated football for two years and I wasn't quite sure when asked by others. Your response would be appreciated.
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Team A has the ball on their 30 yard line. A1 sweeps right and is stripped by B1 (defensive back).

B1 heads for his goal line running by the sideline. Team A player hits B1 at about the 2 yard line. The ball pops out of B1's hand and goes through the back of the end zone without anyone in possesion of the ball.

The white hat signaled a touch back and put the ball on the 20 yard line. (Here is the question part of the play) He gave the ball back to Team A on the 20 yard line.

Now I can understand the touchback and placing the ball on the 20 but shouldn't Team B have gotten the ball?

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