I'm also very confused by this lesson...
The tip in the text of this lesson states "You will never find es followed by bien/mal. However, está can be followed by bueno/malo, but the meaning will be different" (it doesn't really explain what that difference is though).
In the test I checked "Está malo que comas 6 veces al día." (It's bad to eat 6 times a day) as valid and it was marked as wrong. "Está buen que ayudes a tu hermana con los deberes" (It's good that you help your sister with her homework.) was also marked as wrong and it's not easy for me to see why.
It's early in the morning, so perhaps I'm missing something obvious?
Gracias
Geoff