Yes, that really is a tail.

Human embryos develop with a 'caudal appendage' in the womb.

Most of these fleshy additions are absorbed into the foetus before it is born, but on a very few occasions, babies are born with 'tails'. And on even fewer occasions, these tails contain cartilege or vertebrae. Most are removed at birth, but some lucky people have kept theirs.

Singer Nick Cave once claimed he was born with a fleshy appendage. We think he was just telling 'tails'.