I guess he's the son of Player 18.
player19 is a stray horse that bumped you. its just a name for the AI that 'steers' the horse. it already happened to me mid duel that a charger ran over me and killed me. i got the same as you :)
I love you Cochon! I will find this player19 and he will be shamed then executed post haste!
edit: were all the ladies like "ooooOOOOoooo dat shield!"?