There was an explanation of the shorter vacuum nozzle extension during the webcast. Basically it's a choice they will be making when they don't need the performance of the full nozzle they've been flying. These are still getting thrown away after one use, so I can see just saving cost/materials when you can. In yesterday's "deep space update" from Scott Manley, that was his speculation as well.
Since this one was an RTLS launch, clearly they had some excess performance.
Also mentioned in that webcast was that the return of the first stage was done a little differently in that the entry burn was single engine and the landing burn was three engines. It was hard to tell from the video but the return and landing looked normal. This was the tenth flight of that first stage.