Yes, sometimes you just can't put that kind of stuff in the report. The report is read by the client. You could have stated that salt was used instead of sugar.
I used to do Quiznos and the MSC instructed that any health issue was to be reported to a particular toll free number that was provided NOT to the store and not in the report but a separate email to the MSC.
Since the calling about the salt issue was in your report .....your anonymity was jeopardized. The company prolly couldn't use your report because of this. I prolly would have called the store even though another customer might have let them know but I would have not put any info about the call in my report. It is unfortunate because you were acting like a regular customer but msing can sometimes prove to be challenging when placed in these situations.
I did a grocery shop once and the milk case was to be checked. I noticed a carton of milk......partially opened and it had curdled like cheese. I did report it to the manager of the store. I put in my report that I had seen the milk in my report and separately let the MSC know I had told the manager. My report was accepted as the client would never know I was the shopper since any customer could have seen the milk in the case. If I had put in my report that I told the manager, then the store would have known I was the mystery shopper.
So since, the part of you calling the store after the shop was not actually part of your shop..(the shop basically ended when you left)....I would not have put that in your report. I would have let the MSC know in a separate communication(email) about it. They prolly could have still used your report because the client would not have known that you, who called was the shopper since anyone that ordered the stix would have noticed the salt so the client would still be clueless on who the shopper was.