I read this more as... he wants his people to believe that what they are doing is noble, so he must appear to be noble as well. "Aww, man. Sucks we had to do this." will make people feel better about doing something against their morals if the ends will justify the means.
100%. But Solarin played into the already high tensions. He didn't try to de-escalated, he just feigned it. He knew bringing up their dead loved ones in a tense situation would stir their emotions. He wanted to do that, and he was ready for it once he used his cyber-arm to prepare for the expected backlash.
It's all slight of hand. He's smart - I will 100% give him that. He is calculating. To that end, he knew how to get the expected result. He was playing chess while they were playing checkers. He smirked when he saw one of them flinch - he picked his target right there. He emphasized what he just said to turn that knife a little more.
The resistance never stood a chance. Solarin is brilliant, unfortunately. So the losses are going to keep piling up. The MC is going to plan for the next day and Solarin is a month ahead. He is a villain I am excited to watch, honestly, because he can very easily win over a crown with his rhetoric and people who don't believe him are dubbed wrong or traitorous. I half expect him to have some plan to use these 'deep ones' to try to gain power for himself. Maybe it was all made up? Maybe he has more information that we know he isn't telling Aria.
I think that him actually believing he is doing only what is necessary to save the entire universe would be a hell of a twist, but I think there is more of a chance of him just being a selfish asshole.