How does Howling Blade: Resolve work?

Gain the ability to use the finishing blow that follows the forth strike of a swift attack or Blazing Assault at any time during Howling Blade.

The damage of the finishing blow increases in proportion to the number of times a swift attack and Howling Blade have been chained together.

Isn't the finishing blow the Potent Blow button? Isn't the finishing blow pressing the Potent Blow button at the end of Howling Blade? How is this supposed to work?