There were two delays. The first was the logistical problems created by the Balkan campaign that you're referring to, but the second was in the late fall when the advance units were within sight of Moscow. After the initial breakthrough when the Germans surrounded the bulk of the Russian army, they ran to Moscow as quickly as they could. They needed to regroup and gather forces for another attack against a strongly fortified city. That second delay is the delay he said was stupid. Most historians contend it was necessary because it would have been a Little Bighorn kind of disaster if the Germans had attacked.