It's a reference to a meme where people refer to bears and other apex predators by asking, "if not friend, why friend-shaped?" The Friend-Shaped Car is cute without actually having teeth and claws to rend you limb from limb. It just looks friendly, and is no more inherently dangerous than any other car.
I find humor in using odd descriptions, like when I refer to my mother as "The Mother Thing" based on a character from Robert A. Heinlein's Have Space Suit, Will Travel. Spoiler alert: she isn't a telepathic alien. Also, bonus AMA trivia!