Continuity mistake: The landing party beams down in daylight, but the window inside Mendez's office shows that it's night outside. In the next exterior shot, it's day again. Next shot back in the office: night. (00:00:30 - 00:05:20)
Continuity mistake: Kirk introduced Spock as "Lieutenant Commander" instead of "Commander".
Answer: Kirk was getting his physical and Dr. McCoy probably turned off communications, because if he hadn't, Kirk would have left and headed straight for the bridge, leaving McCoy irritated.