What you wrote is what I was expecting - code could be due to a bad KS or a transient software error. If it is the former there should be a drop in mpg, if it is the latter no change in mpg. IMO a 20% increase 'may' occur if somehow the emissions got shut off - not a likely scenario.
The other thing that surprised me is the tech did not read the code I read (P20EE) . . . instead he read a bad KS code which Google Search says ranges from P0325 - P0335. I can understand BMW tech with a better scanner reading more codes than my simple reader . . . but I don't understand why he doesn't read what I read.
As you said what the SA is saying and what the tech is going to write may be two different things.
Yes I will post my service report once I have the car back plus what the tech told me he did.