The Green Button

The rules were simple: you walked up to the black box and chose which button to press. Either the red one or the blue one.
The red one would mean you were going on a trip to visit a cake factory.
The blue would mean you were going to the cup final.
But when it was his turn, Noah saw something unexpected.
There was a red and blue button, but also a third, green button.
Nobody else had seen a green button. Even his teacher could not see one when she turned the box around.
What did it mean?
Was he imaginging it?
What would happen if he pressed it?