Here is from an NCAA booklet about what you have to do to avoid sitting a year so you can play immediately coming from a JUCO. Presumably, using Clemson academic credit, Chad Kelly likely graduated from the JUCO :
IF YOU HAVE ATTENDED A FOUR-YEAR SCHOOL AND NOW ATTEND A TWO-YEAR SCHOOL If you have attended a four-year school but now attend a two-year school and want to transfer to an NCAA Division I or II school, you may use an
exception to compete immediately if you meet one of the following conditions: 1. You want to return to your original school. 2. Your sport was not sponsored at your first four-year school. 3. You have not participated in your sport for two years. 4. You plan to attend a Division II school and have not been recruited by that school. 5. You plan to attend a Division III school. 6.
You graduated from your two-year school.
http://www.ncaa.org/sites/default/files/2017-18_Transfer_Guide_2_Year_20170721.pdf