BS penalty. Int. grounding on Jameis.

I am so confused. Regardless if the time was running or stop, how can spiking the ball a penalty for "intentional grounding". The whole idea of intentional grounding is when a quarterback intentionally throws the away without a receiver nearby to avoid a sack. Spiking the ball was not trying to avoid the sack. What is the ref interpretation of this rule?
https://saintsreport.com/threads/bs-penalty-int-grounding-on-jameis.478974/post-8922140