Jonah only had the message God gave him. It did not include the fact that if Ninevah repented God would be merciful.
What Ninevah did after the display of God’s mercy to incur God’s wrath was not Jonah’s business and not part of his prophetic charge. He was to be faithful to as much light as God gave him at the time and that was to proclaim God’s judgment just as he was told. How it ultimately worked out was God’s business.
So...
Jonah ‘made a prophecy’. Jonah’s prophecy didn’t come true. According to the article above (and Deut), Jonah is a false prophet.
All I was trying to point out is that it isn’t all that cut/dried. Did I make that point? I still believe that Jonah ‘heard from God’ and was a ‘true prophet’, even though the article outlines how he couldn’t be...