If you are a undercover security person at a store if they are one or not?Do they have to tell you the truth?

My son and I have been going to Walmart in our town for years and I have noticed 2 people that I know that they are both undercover security acting like they are shopping they are in walmart for atleast 5 hours walking around and the 2 people said that they are not uncover plain clothes security.They were both rude to these 3 children and I contronted them on it.I talked to the Walmart supervisor and she knew who the 2 people that I was talking about and would do something about them being rude to ohter customer.I would like ot know if by law if a person ask if they are undeover security,do they have so tell you the truth or what?