Nice to know who they’re rooting for. He said “greatest”, not the largest. Barbarossa and the Soviet couterattack weren’t amphibious landings, either.
The Posties know that (one must presume).
The Russian operation was not a military invasion. It was part of a continuing follow-up campaign of pursuit of fleeing forces characterized by both armies having been in constant contact.
D-Day was an invasion, characterized by the need to establish a beachhead in an enemy-fortified mainland in which one goes from no contact with the enemy to immediate contact. Literally, they went from zero presence to a huge beachhead in the matter of a month.