the answer is: ninas behavior is best explained by the circumstances surrounding the encounter
Situational attribution refers to the collections of effort that people do in order to understand our experience (the things that happen to us.
In this situation, Jorge probably see the way Nina behave during the encounter (whether she smiles, happy, or uncomfortable)
After observing it, Jorge tries to attribute why Nina is behaving that way and correlate it with the person that she encounters with or the type of conversation that they have.