I think 'maybe' you were right with your suspicion regarding the cop in the store, but maybe he came in to get something and noticed your sidearm then. As for the park incident, I seriously doubt they were sitting there for you. I mean, you spotted them parked there from 100 yards away. Do you really think if they were called for a MWAG they would just park somewhere and hope the subject happens to walk by them? My guess is it was pure coincidence they were there, and that they pulled off shortly after you walked past.