not sure if this is a known bug or not but its the first iv ever seen him after completing main compainions questline ages ago. i walked into the mead hall and there he is sitting at the table eating a piece of bread. when interacted with, no dialog box appears he just says generic lines about the compainions. again i dunno if this is a know bug sorry if it is. im running v 1.8 and have downloaded dragonborn if that matters

it happens

I'm not sure this is helpful, but random not-dead NPCs have appeared in my game, as well. Once I was at the College doing a Master quest for destruction when RANDOM NAKED ANCANO showed up and attacked me.