Matt is (likely subconsciously) mirroring Shiro in smashing his emotions down and being strong for Pidge. There's obviously emotion there, but he's not dealing with his own.
I've also noticed that he's keeping his distance from Shiro (or the reverse). My guess is that either he realizes something's up with Shiro, or he just doesn't know how to interact with him after everything.
3. Something to do with Shiro. That, to me, is the least likely. I'm not entirely sure what this would mean. I think he would have reacted differently, or brought something back with him.
Also, whatever was in there actually pissed him off. He's been showing so little emotion other than soft concern or determination or excitement, that it's noticeable to me.
Quinn: I'm kinda busy...
Matt: Kinda busy, Dad!