RLER's Poco: Is he playing with his invisible friend?

Here at Ranger's Legacy Equine Rescue, we sometimes see some strange and surprising behavior from our horses. This is one of those times. This has to be the strangest behavior I have ever seen. This was taken December 26th 2014 just 11 days after Poco's best buddy, Red, passed away. Poco was not sick here. After taking this video, I completely checked him out. Everything about him was completely normal............ except this behavior. I have even had my vet look at this footage. He was baffled. Was Poco having one last play date with his buddy? What do you think??