Just like Jannes said, NameCheap is a partnering registrar with Afternic. That means if someone lists their domain for sale on Afternic, it will appear on all their partnering registrars, including NameCheap, GoDaddy, DynaDot, and Others.
Someone previously owned the name, listed it on Afternic, and then forgot to remove it after they let it expire. If someone were to try and buy that name through NameCheap the sale wouldn't go through. You can contact Afternic and show proof you own the domain (a screenshot of it inside your Epik account) and ask them to remove the listing. They will, and then it won't appear in the NameCheap search anymore. You'll have to do this anyways if you plan on listing it inside your own Afternic account. Hope this helps!