Another possibility: He was punched exactly when the cinema started. When you're hit, health doesn't lower instantly, it's more continuous... Maybe his health was being lowered and it was interrupted by the cinema, so it didn't stop being lowered... Dunno, there are a lot of possibilities, PD is just a reandom game full of bugs everywhere... It could also be that once the cinema starts guards have some time to react... No idea, but this has happened to me before, and more than once iirc (not sure if in Agent and full health, though). Other things that happen are a troll guard blocking the safe door, a troll guard blocking the room door, so that when cinema ends you expect it to be closed but it's open and 2 guards are chooting at you, etc.