Most weapons people wield have a distinct feeling and were inherently different. From this, when one wields their weapon the Spiritual Qi would take on that feeling and sensation. Even if one was using a club the feeling of one’s Qi would take on a blunt and heavy pressure.
When using the sword, the feeling of a person’s Qi would be fast and sharp, making it known as Sword Qi. Blade Qi was more forceful and straightforward in nature because of the way the weapon was wielded. Only one side of it was used for attacking so a blade wielder had to maneuver their wrist to attack their opponents at each turn. They had no choice but to be forceful and overbearing while attacking, and if they slip up, it could lead to their disadvantage.
Sword wielders were different as both sides of the swords were sharp so they have numerous options of how to attack an opponent. They could be as flexible as they want to be.