Normally, it will download all the media for the citations plus any media you have added yourself to your online tree. I'm guessing that FTM may not have finished downloading all the media the first time and picked up when you sync'd again.
You can check the counts on your online tree to see how many photos and stories you have there and compare to what is showing in FTM.
On Ancestry.com, look at your Tree Overview and see the count of media there (photos and stories).
In FTM, on your Plan view, click the button "More..." on the sort of upper left, next to the name of your tree to see more details about media and other stuff.
The counts won't match the counts in FTM though because they count different things in different ways. It can give you a few clues though.