The Battle of Antietam did not happen by accident, it was carefully planned, which turns the focus on Lee himself, the kind of man, general, that he was. He didn't wander around in confusion. He had a purpose, a mindset, an objective which he realized through maneuver.
If McClellan had seen through the ruse and had the courage, he would have raced straight for Crampton's Gap and Harper's Ferry, determined to wipe out McLaws's two divisions in Pleasant Valley and try to get between Lee and the Potomac, crushing Lee before he can reunite with Jackson.
If nothing else was certain, the movement would certainly have forced Lee to race for Williamsport and get back into Virginia. At which point, using the Ferry as his base, McClellan (if he had courage) would move toward Winchester to engage Jackson and Lee.......... Author Position Paper