I would fold this for all the reasons you stated. Plus I am generally not comfortable sticking my whole stack in facing an all in overbet with only one pair. The player could be assuming you're trying to bluff the king on a dry board here or he could assume you do in fact have the K and is trying to get you to pay off his made hand. I would suspect which line he is most likely taking depends on your image at the table. Given no additional information I fold.