Terrorism is the intentional use of violence toward an unarmed population for the sake of a political ideology.
Since Islam is a political ideology that was not only openly embraced by the shooter, he was also wrongfully proselytizing it toward his patients and even promoting it in his presentations to medical staff.
You are clearly the type that thinks Islam is nothing more than a religious preference, when in reality it is a legal system (Sharia) and political ideology as well.
Certainly the Fort Hood shooting was terrorism: 1 bad guy shut down the entire Nation's military communities with increased force protection measures, and paralyzed the military with effects that will reverberate for quite some time despite the whitewash and falsehoods oozing out of the hierarchy. Certainly the Fort Hood shooting was terrorism: the entire Army community now lives with anger, frustration and distrust throughout the weeks/months and potential years after Hasan shot several great Americans dead.