The good thing about the nhl and nfl concussion protocol is that its very hard to hide concussion symptoms. You take a baseline test in the offseason, and then after suffering a potential concussion you take the test again and your ability to recall is measured against your baseline. Its a pretty accurate indicator.
I suspect he did note suffer a concussion in the previous game. If he was fully dressed and in the pressbox exposed to lights, sounds, smells and engaging in conversation then It is likely there was no concussion.