The case book has:
"7.3.5 SITUATION F: With R1 on third, one out and two strikes on B3, B3 swings at and misses the pitch. The ball bounces off F2’s glove into the air, where it is hit by B3’s follow-through. The ball rolls to the back stop. B3 reaches first base safely and R1 scores. RULING: The ball is dead immediately. B3 is out for interference and R1 returns to third base. A batter is entitled to an uninterrupted opportunity to hit the ball, just as the catcher is entitled to an uninterrupted opportunity to field the ball. Once the batter swings, he is responsible for his follow-through."
and....
"8.4.1 SITUATION H: B1 swings and misses a pitch for strike three. As F2 is attempting to catch the pitch, B1 hits F2 with the bat on the follow-through, hindering F2’s attempt to catch the ball. RULING: B1 is out for interference."
So I think you called it correctly (in FEDlandia).