The author does this again here:

What about World War II, though? Surely that’s Stalin’s ace in the hole—that no matter how many people he purged, how many socialist movements he wrecked, or how much of a bigot and philistine he was personally, his “tough decisions” were the crucial factor that won the war. Stalinist authors like Furr and Ludo Martens devote many pages to the war years, and there is one thing they’re right about: the Soviet Union, more than any other geopolitical group, was responsible for breaking the back of Nazi Germany, and destroying Hitler’s empire of madness and death. The images of Red Army soldiers throwing open the gates of Auschwitz will live in human history forever, and at Stalingrad alone, more than a million of them gave their lives—more than the U.S. lost in the entire war. But crucially, these are not Stalin’s victories, nor his sacrifices. He, like Churchill and Roosevelt, was sitting safely behind his desk when the real heroism happened. To credit him with “winning the war” or “defeating Nazism,” as if he personally parachuted into Berlin with a belt of grenades and started blowing up bunkers, is to erase the collective struggle of millions, and to surrender to the deeply conservative “great man” theory of history. Supposed Marxists should know better.

Stalin didn't personally shoot all those people who got executed either, but the author didn't hesitate to blame him for them. Are leaders responsible for things or not? I guess in the case of Stalin he's to blame for bad things but can't be credited for good things because he's Bad.