The Lord had just spoken about prophets that would prophesy a lie to the children.He told them what would happen and what the false prophet would say to deceive them. 
Along came the prophet, Hananiah, and made his outrageous false prophecy. He did it in front of all the priests and people. He had no shame. 
Thankfully Jeremiah, a prophet of God, called him out on it. 
Boldness and confidence are persuasive. But just because someone is bold or confident doesn’t make them right.
Stick with what the Lord has shown you to be true, no matter how persuasive, or enticing the false prophet may be.