Heat energy goes from the kitchen into the freezer when Steven opens the door because heat flows from warmer to cooler areas to achieve thermal equilibrium.
When Steven opens the freezer door, heat energy flows from the kitchen to the freezer. This occurs because heat always transfers from a warmer area to a cooler one to reach thermal equilibrium. The concept is similar to an ice cube melting in a drink; the second law of thermodynamics states that heat cannot transfer spontaneously from colder to hotter. Therefore, the kitchen, being warmer than the freezer, loses heat energy which then moves into the freezer.
Moreover, when the freezer's door is closed, the freezer works to remove any heat that enters, and transfers it outside into the kitchen to maintain a low temperature inside. This is an ongoing process to keep the freezer's contents frozen. When Steven opens the door, he briefly interrupts this process, and some of the cold air escapes as warmer air enters.