It's natural for people to have a higher degree of acceptance for anyone who claims to be a fellow employee, and who knows company procedures and lingo. The social engineer in this story took advantage of that by finding out the details of a promotion, identifying himself as a company employee, and asking for a favor from another branch. This happens between branches of retail stores and between departments in a company, where people are physically separated and deal with fellow employees whom they have never actually met day in and day out.