Tanner's timeline:
2015 season - playing as a "true" freshman
2014 season - mission
2013 season - mission
2013 spring - attended & practiced
So you are correct, he had a spring camp in the new offense. But he didn't have a full year. Regardless, the offense he's running now is not what was being implemented in spring 2013; which was full Go Fast Go Hard.
Either way, he did have some minimal exposure to the offense prior to this fall camp, which shouldn't diminish how remarkable his play has been.