According to the author of the book of 2 Kings, God is telling the bad king that the people of Jerusalem are not afraid of him and are even making fun of him. They know that God is stronger and will protect them.
2 Kings 19:21: This [is] the word that the LORD hath spoken concerning him; The virgin the daughter of Zion hath despised thee, [and] laughed thee to scorn; the daughter of Jerusalem hath shaken her head at thee.
This verse is parallel to 2 Kings 19:21, rather than contradicting it, as both describe the same event about the daughter of Jerusalem.
Isaiah 37:22: This [is] the word which the LORD hath spoken concerning him; The virgin, the daughter of Zion, hath despised thee, [and] laughed thee to scorn; the daughter of Jerusalem hath shaken her head at thee.