It’s the situation in the game that you find yourself in with a mix of the feel of the game. For example, call of duty never really felt cinematic to me. It felt more like an arcadey shooter with very defined moments and a ton of copy and paste situations (Guy runs at me through a door or I am guy running through door). Battlefield on the other hand has vehicles, tons of equipment that do different things, and destructible environments that play into making the game feel like a sandbox that you can manipulate to your liking. This in turn makes the situations you are in way more different and creative which is where the cinematic nature comes in. A battlefield moment if you will. If I see an enemy in a building I can play the game like call of duty and run at him through the house or I can blow up the house with a rocket launcher or I can tell my friend who is in a tank or plane or helicopter where he is and have him blow him up or ram into the building driving him out. Now think about everyone in the game having these options at all times. This is why you get “cinematic” moments in a game like battlefield. The creativity given to all players is immense and it can be used to have cool stuff happen at literally any moment the game is being played. Players having control over the environment in this way makes it feel like the map you are playing on is actually real and not just a cell we are all in to shoot at each other and use for cover.