I have a feeling it's Beth in the forest that Darryl is talking to, and Carol got left behind. I think the next episode is mostly flashbacks to the whole time Beth has been gone, and then at the end of the episode (or the episode after that) Daryl and Carol show up and rescue Beth, but Carol gets caught/killed in the process. Beth is mentally traumatized, so she's hanging back when Darryl walks up. The rescue took place while they were gone for the events in this episode.
I don't have a lot of info to back it up, just something about Darryl's reaction to the question 'where's carol?' and then him seeming to talk to someone he's friendly with behind him, like 'hey.. it's ok, you can come on out now'.
The only other explanation I can think of, is that it's that black dude from the first episode that we got a sneak at a few back at the very end of the episode. I can't think of his name right now. The 'clear' dude that went crazy after losing his son. I feel like I remember Darryl met the guy, but either he figured most of the camp doesn't know him and he wouldn't want someone freaking out about a new guy before he introduces him, or the guy is just super nervous about meeting new people and was hanging back.