That’s funny. Luther said many things. That’s why I love him. He said some really stupid things at time, for which he would be the first to admit. Luther is capable of saying just about anything. I would be very interested in where you found this citation. I have never read it or heard of it before. I would like to read the quotation in context, for Luther often used humor and sarcasm in his writings and sermons. Luther also gets accused of saying things which he never said.
Be thou comforted, little dog, Thou too in Resurrection shall have a little golden tail
Perhaps you can put this into the proper context? Martin Luther's suggestion that a little dog take comfort in Resurrection?
I honestly don't see any other interpretation, than the literal meaning of his words.
There is a considerable body of writing from John Wesley and Matthew Henry on this very topic, so it's not exactly a fluke that Martin Luther would believe so.