Classic decorticate posturing after the hit.
https://www.ncbi.nlm.nih.gov/books/NBK559135/
Decorticate posture is an abnormal posturing in which a person is stiff with bent arms, clenched fists, and legs held out straight. The arms are bent in toward the body and the wrists and fingers are bent and held on the chest. This type of posturing is a sign of severe damage in the brain.
And his poor fellow was CLEARED from concussion protocol too soon. The NFLPA will soon NOT e too happy with situations like this.