The key, at least from the umpiring standpoint, is where everything was in relation to the wall. If the hand and ball were on the stands side, it was merely a very stupid move on the part of the guy. If they were on the field side, it is by definition fan interference, with the "penalty" left up to the umpire. Based on Alou's positioning to make a catch, and the example given in the MLB rulebook, it should have been ruled an out in that case.
Damn the curse anyhow.