I'm sure that you think he was a 'really nice guy' like Trump and you defend white supremacists.And there is no evidence he targeted any specific group, or killed any specific group.
Add to that his statement after the killings (through his lawyer) that he was extremely remorseful. Whether you believe that or not, it's the not the type of statement a terrorist makes. Terrorists take the opportunity to push their ideology and justify their actions with it. You know, statements like "Allahu Akbar", as the Pulse nightclub shooter shouted.
We don't know yet for sure if he really was a member of a white supremacist group, only that he was himself a violent, racist, right winger.
https://www.cnn.com/2018/02/16/us/exclusive-school-shooter-instagram-group/index.html
Meanwhile Trump is now backing arming teachers, his response to meeting with students who wanted gun control.