The kid in the cage is obviously not Chico. It is too obvious (intentionally mind you) that all this video is made to deceive and mislead us.
The guy from PAX saw this video for the first time, much like us, he THINKS this is Chico.
Plus the highly ranked burned man keeps saying "Chico and Paz" "Chico and Paz" ... of course he wouldn't mention his name so many times if the kid in front of him was Chico himself.
He would probably say something like "the kid" "the brat" etc..
And since Big Boss is far older than Peace Walker, and obviously returned from some retirement - as suggested from - "well done Snake, age didn't slow you down a bit" - we can safely believe we WILL SEE SOLID SNAKE, perhaps in his early days, training/advancing in Foxhound.
So yeah, an awesome debut between Solid Snake and Big Boss? well yeah... it hasn't happen since the 80's - what better timing and place could it be for such an event?