What
Before this change, updating a plugin always fetched its repository, meaning it downloaded the plugin's source. The update can now return "up to date" without fetching, either because no check was made or because no fresh download was needed. It can also note which repository the plugin comes from without downloading it.
Why
Plugin updates can finish faster when there is nothing new to download.
Something disagreesSomething we can check disagrees with this entry, or the writer said they could not settle it.
The writer flagged doubt
It is not clear under which conditions the download is skipped.