Well, my very first gas station with photos audit that I ever did I did two days in a row because I failed to get the inside register receipt. So you could always just say, "Maybe the first auditor missed something they were supposed to check so they needed it done again so the report would be complete." That shifts the focus off whatever the station did wrong and puts it on maybe the shopper did something wrong.
Whatever you do, you don't want to get into speculating about the station. A simple, "They may have missed one of the pumps the first time through so I will be extra careful" should be enough.
But it's silly for them to fuss about "going through this again" because other than answering a few questions, it's the auditor who is going through this again, not the manager. All he has to do is sign a piece of paper saying yes you were there.
Methinks he protests too much. Which may have a lot to do with why he got reshopped.
Time to build a bigger bridge.