flinging the notebook

[TheMan_WithNoPlan]

If the ghost flings the ghost writing book, does that rule out that evidence?

[underscores222]

It means the ghost will not write in the book. Depending on settings, there's two different reasons.
First, if you are playing with all three evidence, then when the ghost throws the book, it means it is not a ghost writing ghost.
However, if you are on harder difficulties where the ghost does not give 3 evidence, then it simply means that ghost writing is not one of the evidence you will get this round. Since the ghost only gives some of the evidence, that means it could still be a ghost writing ghost that simply isn't giving ghost writing this time.

[CovfefeCat]

The ghost can still throw the book if it has writing as an evidence.

But if Writing is an evidence type, it will always write in the book when it throws it. So you can remove a bunch of items in the room as incentive for the ghost to touch the book, since the Write action is normally a separate, lower chance than a normal interaction.