VERY SERIOUS QUESTION offence accusation?

This is a case of slander. The store manager, right or wrong, had not right to come out and accuse your grandfather in the manner that he did. Trying to confie the phone like he did could also be considered harment. I would not only contact the district office of the company in question, but also talk to the authorities about a harrment claim. Something like this should not be tolerated. If the manager had legitamite concerns about your grandfather, he could have taken his plate number and called the police. This is still a country where people are innocent until proven guilty, although some seem to forget this.