In the summary below of episode 158 of the series Black Clover, how did the Spade army lose?

Context: Ralph continues trying to cross the border. The Spade army begins crossing the border in a mechanized citadel called Candelo powered by siphoning magic from Spade commoners. Asta, who has grown even stronger and can now fly astride his demon slayer sword, flies to Candelo where he is enraged to see Spade Knights siphoning prisoners to death. Asta confronts Candelo’s commander who reveals he is also the vessel for a devil. He poisons Asta with poison magic but Asta easily absorbs the poison into the demon destroyer sword and furiously cuts the citadel in half, defeating the captain in a single blow. The Bulls arrive and Mimosa helps the prisoners recover. Noelle reveals Luck and Leopold were sent to destroy the Spade base near to the prisoner’s village. Realising they get to return home safely the prisoners reveal the Spade kingdom is ruled by the Dark Triad, each possessed by a powerful devil, and their followers the Dark Disciples who draw demonic power from the Triad. The Triad, siblings Dante, Vanica and Zenon Zogratis, consider the loss of Candelo trivial when they are close to their goal for which they only need capture two Arcane Stage mages. Ralph finally crosses the border and collapses by Hage Church where Sister Lily finds him calling out for “Prince Yuno”.

Answer: Asta countered the Spade Kingdom's commandor's poison attack with the demon destroyer sword, then cut the attacking citadel in half, defeating the captain in a single blow.