No. The store is not outing mystery shoppers. Unfortunately, you have outed yourself. You've mentioned that you've informed the scheduler that an employee (and store manager) found your behavior (or appearance) to be suspicious. The employee AND manager remembered you from your previous visit. Whether or not they exclaimed "You're the mystery ... More @Wikipedia
Hover over any link to get a description of the article. Please note that search keywords are sometimes hidden within the full article and don't appear in the description or title.