Sort of correct. For super simplicity sake, say you have an app that has 10 files. An update to the app changes 3 of those files. So OTA would basically copy the 3 new files over the 3 old files with same name effectively removing the old files completely. Now a full install of said app (IPSW) would also overwrite those 3 files but will also recopy the 7 files that were never changed in the 1st place. So technically you are left with the same set of 10 files either way.
In a nutshell again a very basic explanation.
This is also my understanding from back when OTA was first introduced. However, I also don't work for Apple either so.........