The seller is dropshipping and does not know what his supplier's stock is like at any given time, nor can he be sure when, if ever, the product can be supplied.
It is also possible that he has never seen the item and has no idea what he is actually selling.
Get your refund and leave appropriate feedback and Detailed Seller Ratings. A normal completed transaction would get Five Stars while the lowest DSR is ONE star for communication, description, prompt shipping and shipping cost.