Well, he doesn't know a lot about Armin yet, but he's obviously a smart cookie, which is kind of weird because now he knows Armin is under his command and he's pretty sure Armin is smarter than him. He sure as shit trusts him more than his other castmates at this point, though he doesn't know the scoop on Galen yet. He'll definitely be keeping an eye on him from now on, because he won't trust Cross and Liter not to pull anything until some time has passed without them being a problem, and while Armin is obviously intelligent he's still pretty sure they could easily beat the shit out of him.

It looks like Armin has also received the tiny bodyguard bonus (if he considers it a bonus...). And soon he'll find out the two of them are the only ones from their world who aren't titans. That will be fun.