"Oh, uh -" Well, that's unexpected. They've had a lot of people asking about them since they've come back - more permanently; they stopped in now and then but not to the extent they had been present in the District before, a daily fixture - but that was all people they knew. They're fairly sure they've never seen this guy before. They'd definitely remember the shirt. Unless this is a figment of their imagination, but usually those aren't so lucid. They tend to be more abstract...
"Um, I'm sorry, my memory is not so good - have we met?" Come to think of it, he certainly sounds familiar.