I did wonder about cause and effect
Why would the first fire bird pick up a burning twig?
One possibility; thought it was a cooked snake then dropped it when it wasn't.
Another possibility; picked up a smouldering animal then dropped it because it was too hot, or just to settle down and eat it.
There must be a common use case for moving burning things before the admittedly smart birds can see the effect of dropping something that is smouldering and seeing fire start, and making the intuitive leap that results in the consolidation of observed behaviour into learned behaviour.
Could make future fire insurance claims interesting as well. Bloody bird done it, mate!