Who are all these girls on my fiance's skype?

So, apparently my fiance left his skype logged in on my phone, because when I got out of the shower, someone had tried calling him on it and when that happens, it automatically opens the app on my phone. I scrolled down the list of convos, and saw all these random usernames that I have never seen before. I'm a little confused because I've been on his skype before (we use it to talk to his parents accross the country) and they weren't there before. When asked, he claimed he didn't know who they were or why they pop up, and that he's tried deleting them countless times and they keep showing up. He says his email's linked to so many things like outlook, xbox, ect. and he doesn't know where they synced to his skype from. He's been out of town working for the last 3 weeks and I just have that feeling that something isn't right. None of them have any convo history on skype, but this is oddly suspicious. Does anyone know what could be happening?