Well, he chases after the cats, and Idgie has never actually seen a dog, so even though he is small, he is still bigger than she is, and therefore scary. The other cats had all known Joey, who was afraid of them so they are just annoyed and frustrated.
It is. :3 I thought of the name when mom mentioned her cousin's dog (who is named Penny). My mom likes to name our pets after characters in movies, books, TV shows, etc, usually when the pet reminds us of them (like Miss Kitty), or if it just is a name we all like (Boscoe)(Max is the only living one without such a themed name, since he was given to us by my mom's cousin, and Joey was named such just because it was more fitting than any themed name). So I thought of Desmond from Lost, which we all liked.
Coincidentally enough, Desmond's wife was named none other than Penny, on Lost. XD