This is what I found on the internet concerning this example.
http://www.bafra.org/rulesctee/rule.../interp2-10.htm
SECTION 7. Responsibility and Impetus
"VI. Team A punts. The ball is touched by Team B (no impetus added) and crosses Team B’s goal line. Then Team B falls on the ball or the ball goes out of bounds from the end zone. RULING: Touchback. The same ruling applies if a kick in flight strikes Team B or merely is deflected by an attempted catch. Team B may recover and advance, and
it is a touchback if a Team B player is downed in the end zone or goes out of bounds behind the goal line (Rule 8-6-1-a). "
I thought that it was made pretty clear that it should have ben ruled a touchback.