Where is the customer field got populated?

We are using EBS 12.1.3

In the system administrator responsibility->security->user->define form there is a field called customer. When we created the user, we didnot put anything in this field. I just saw someone's name got populated to that field. I checked the help and record history and the updated by to the FND_USER table is the user herself. She does not even happen to have system administrator responsibility and should not have the access. I am wondering where else could this field be populated from? Gurus, please advise. Thank you very much.