Moriarty initially needs binoculars to see the statue from his faraway-rooftop vantage-point, and so his two dim-wit hench-dogs couldn't have talked about the statue in such knowledgeable detail, since they themselves don't have binoculars with them and presumably they haven't seen the statue up-close yet.
Moriarty has to cut loose the sand-bag to release Lestrade from the balloon's basket, yet the bag is never shown to fall along with Lestrade and his hat.