The last message it gave me in limbo was: Be careful, though, as there are things that live in limbo. LIKE WHAT LIVES IN LIMBO I TURNED ON SUBTITLES AND THEREE WERE ONLY MY OWN FOOTSTEPS
Don't worry, there's nothing that truly lives in limbo.
On an older version of limbo, if you stayed there for long enough, you could be greeted with the message that "Herobrine joined." While it is unconfirmed, that is what is believed the message you described refers to.
