Pay attention to the gentleman over Strzok's left shoulder. He'll hand him a note, there's a little stally-stall-stall, then he goes right into the script.
Stay paying attention to to Mr. Note-handover guy's mouth at 25:42. That's when I first noticed it then he started to get more obvious. He can't help himself from mouthing certain words of the "response". He even catches himself being too obvious at 26:00 when he says "war hero". This continues to 26:34, it cuts away, and it seems everything Strzok was saying at that point was ad-libbed or just his own personal commentary.
Scripted af.