Sieging refers to destroying enemy structures (towers, inhibitors, nexus). In Wukong's case with Divine Sunderer, I believe they mean that you can always use the item's passive bonus damage to poke enemy structures safely and take them down quickly.
The bonus damage from Divine Sunderer goes together nicely with Crushing Blow. This results in a lot of damage and the quick destruction of enemy buildings. 😁
The bonus damage from Divine Sunderer goes together nicely with Crushing Blow. This results in a lot of damage and the quick destruction of enemy buildings. 😁