You mentioned that you have no idea of Stanley's early life. I think it is quite likely he was severely ignored or even abused during his youth, resulting in what in humans is called "failure to thrive" syndrome. I am not saying this as a "put down" of Stanley, but in his brain certain cognitive circuits were never developed. That doesn't make him any less adorable, and it doesn't mean that the love you offer him is not returned a hundredfold in his heart.
"Good Boy, Stanley! Go find Doctor Livingston!"