As a KGB operative he has been extensively trained to control his emotions, and not to be overruled by sentiment. The second training an agent has to go through is to wear a mask of the expressionless face in totality - eyes, lips, nose, ears, facial muscles, movement of arms, legs, body posture, and very importantly voice. Or to wear a face as per the need of a task. So if Putin needs to show anxiety if his face, he would portray anxiety, if he needs to portray warmth, you would see a genuine smile They are extensively trained in reading body language, and voice, as well as controlling body language. The best of the secret agents would never get caught on a lie detector machine. Their thinking is seamless and does not trigger any pulse movement for detection.
I am putting a few pictures to understand his body language, and what he wanted to portray..
Most nation heads are imparted sessions on body language, but they get it only after assuming office, so it's difficult for them to master it. Which is not the case for Putin. Putin keeps on assessing his opponent's live, apart from having extensive homework ready.
He thinks like a chess player keeping his moves and countermoves ready in anticipation of all possible moves by the opponent. It is extremely difficult to surprise him. He is in a position to know about the possible outcome well in advance, as such you wouldn't find him tense. He is prepared for all possible eventuality well in advance. People could be cool only when they know what is coming up. So he is calm. And even if he's not calm, you wouldn't be getting any sign in his face or body language. He doesn't have to do it deliberately, it comes off automatically. For others, the process is not natural. So we see lots of facial expressions.
Very importantly there would hardly be any leader in the world of his stature with so much experience in office. He is in power since 1999, four terms as President and one term as PM apart from his long service career of 16 years. Being in power for a country like Russia with critical internal as well as external dynamics, there would hardly be any situation that would take him by surprise, or which would seem new to him.
Image source - Google.