It's a fair assumption to make, really. I mean, who actually enjoys being confined?

Though could be he also thought you might cause trouble once you were out, since sometimes that expression implies that, too. You might've been an unknown factor that Mr. By-the-Book wasn't sure how to handle back then.

[Despite being unsure of Aya, himself, that thought does get an amused smirk out of Rex. He's definitely caused his share of trouble for strict rule followers and authority figures.]