Lex Talionis
Mattheus resumed the act of being off-balanced from contact with Artorius Morgaine once he found Illarion Snowe waiting for him at the Crown residence after the marquess couldn't catch him when he fled the restaurant. It was actually not that difficult, because seeing the Crown Prince had greatly irritated him. He also had the incentive to lean on being a traumatized bully-victim lashing out, as he was still uneasy about the platinum-haired nobleman asking that question again.
Yeah, the entire conversation at the restaurant was upsetting and he wasn't acting out nor faking the emotions.
But he was able to twist things around, using Artorius Morgaine and Kelsey Norick's actions as a solution to keep suspicion off the twenty-year-old for what would happen soon.