On the one hand, Magnus is used to being disappointed by father figures who he loves. On the other hand, Hanguang-jun isn't his dad, no matter how much (in Magnus's heart of hearts) he fills that role now. Usually he's much, much better than Magnus's dad. In particular, he's proven, time and again, to be reliable. Maybe this is why it stung so much, to learn he hadn't thought to ask about Magnus.

But he's reliable. He's made up for the slight. As hurt as Magnus's feelings are, he can't deny that Hanguang-jun immediately went above and beyond when he realized that Magnus might want a message, too. Shouldn't that matter more than the thought not occurring to him in the first place? Why does Magnus still feel hurt? "Thank you for playing it again," Magnus mumbles, muffled partly by Hanguang-jun's robes. "I know you don't like him." He means: he's glad that, additional useful questions aside, Hanguang-jun's care for Magnus outweighs his distaste for Shen Yuan.