Hearing the approaching footsteps doesn't say much to Derek in a place where tons of people are moving in on the same day. It's when he hears the voice and assumes it's addressing him, given his situation, that Derek stops and takes a step away from the door, looking over to the source. His eyebrows lift a little with interest at the comment. It's kind of nice to know he's not the only one running into this issue, at least...

"Is that what you did?" he asks, making the assumption that this man's had the same issue and that's why he's starting the conversation. It'll probably take Derek a short while to remember that normal people start conversations with strangers all the time and don't do it just because they want to kill them. He'll get there, but until then, he might be a little awkward about it. At least, he thinks, he's spent his entire life pretending to be something he isn't, so he's good at hiding it.