Michael,
Interesting theory (a la 6.05(h) ), but I don't think I buy it. Because it would give the batter license to "hold" his follow through in a way designed to hinder the catcher's ability to throw.
I found a video clip on mlb.com and I definitely would have called it backswing interference.
Baseball Video Highlights & Clips | ATL@SF: Glaus lines an RBI single to left field - Video | MLB.com: Multimedia (2nd row, middle clip)
It looked to me like the PU simply didn't see it - he was pretty well screened by the catcher's body. After the throw, you can see him look down to check the batter's feet to make sure he's in the box.
JM