Does not matter how long someone has worked. What matter is what is expected out of each employee.
If MGT is worth anything then they have guidlines on what work is expectd based on pay/exp. If XYZ is what they expect out of new employees; my question stands, was he doing his job?
If you're a fresh out of college you need to prove that you are
#1 competent (this includes being professional)
#2 reliable and available during specified work hours
#3 able to do what you're told
As a new employee, how can anyone trust you with doing your job and being AVAILABLE during work hours if you're never around and no one can reach you? It sounded like no one knew where he was when he left and he never gave anyone any notice on how to reach him while he was away. Once you are able to prove 1-3, then people can trust you with working at home or leaving a early.
Even if you are allowed to leave early you should only charge the amount of time you worked. If he didn't work 40 hrs then he shouldn't charge 40 hrs. If he finished his work in 4 hrs and decides to leave work then fine, but he should only charge 4 hours worth of work that day unless he stays in the office or continues working. Maybe the manager was waiting for him to finish his current work so he could allocate him some other tasks. Charging hours that you didn't work is a big offense.
Work flexibility is also part of an employee's benefits package. Here where I work, many people telecommute if they live far away and only come to work for certain meetings and when needed. However, they also are worth keeping, available during WORK HOURS, and reliable. Thus, the company values them and allows them to do it.