More info in this story. Looks like the shooter may have been outside when he started shooting at people (according to the injured girl’s Dad). That would explain why the good guy took him down outside of the restaurant.
Sounds like the suspect shot them in the back from the tree line/parking lot out front, as they were walking into the restaurant.
The suspect either knew the victims, or the suspect is simply another nutcake. Could be terrorism, but I doubt it in this case.