This. I don't think they're completely unaware of emotions. It's more likely that their volatility and lack of complete control over said emotions lend to their seeming indifference (and that's putting aside the possibility of Aechmea omitting certain details out of convenience in convincing Phos). They're emotionally stunted, but that doesn't necessarily mean they don't grasp the impact and significance of certain situations depending on their priorities. Like you said, the fact that they've applied psychological tactics towards Sensei gives weight to this notion.