The Ralts line are the Emotion Pokémon, and have very strong empathic capabilities. It's very likely that they smother their own emotions around strangers or those that they aren't comfortable with, and so appear stoic and emotionless to the outside, but once they are around people that they are fully comfortable opening their emotions to, then they are able to free themselves. It's really a shame that they haven't worked out outward responses to friendship ratings in the game models yet, because I could see this Kirlia being very close to someone. She has a beautiful smile and a gorgeous portrait.