note they use updates for both things.
If the gameplay updates were so diffrent from the normal updates wouldnt they call them something else to show the diffrence?
They do and they are. Thats why one is that is an engine change is called a title update, and incremental gameplay updates are background updates via live updating.
Title updates are updates that feature engine level changes and also any gameplay changes ready at that point. These require the user to download an updated file from the network and apply it prior to play. This is because they require an executable update in order for the engine level changes to take effect.
Incremental gameplay updates are background changes made to gamedata without requiring a download prior to play. They happen in the background and dont require and executable update to be used.
Its hard to find in google searches due to the number of nonsense and garbarge across the web since launch with similar tags. Its there though, its just a bugger to find I frankly cant be bothered to wade through pages of searches to it.
Im sure plenty of other users here are more familiar with the article I mentioned and have a link.