I tested an SC with a Sword of Swiftness, fighting a bunch of Heavy infantry. The SC did not have a bless or quickness. The 2-attack sword was his only attack.
In any given round of combat, the SC would occasionally strike two different units in the same square with his sword, sometimes without even killing either unit (though he did chop off one guy's arm and leave the other with a gaping chest wound
). So Sombre is right, it's not true that all attacks from a single weapon may only strike one target. A single weapon can target multiple enemies in the same square.