They're both trying to protect themselves, the difference between them being that Tadashi is still willing to cast that protection aside in favor of doing what he thinks is best for someone else. Even if that someone else wants nothing to do with it.

"You're being careful, aren't you?"

Because he has to ask. And imagining trying to survive among that crowd himself is just laughable. Even for the professor Tadashi had once known, it just doesn't seem to fit.