The info tab shows that your iMovie is called iMovie9.
Is it possible that you have changed the name from iMovie to iMovie9.
I am pretty sure that it would have been called just iMovie when originally installed.
This might be the reason that the Update cannot see that you already have iMovie because
you have " iMovie9" not "iMovie".
As Rich has said " if it ain't broke then don't fix it.
But if you did want to pursue trying to update to 9.0.9 then you could try the following.
First you would want to duplicate the application without changing any names and place in a separate folder on the desktop for safe keeping.To duplicate ctrl click on the application and select duplicate
Take the original ( not the duplicate) iMovie9 and change name to iMovie.
Now try the update procedure using the downloaded 9.0.9 update.
If this works you will have 9.0.9
If it does not work you will still have version 9.0 in the folder on your desktop, which you can place in your Applications folder.
If you want to be absolutely sure of not loosing your current iMovie version then as well as having a duplicate, ctrl click again on the original application and select Compress which will give you a zipped copy of the application.