Two weeks ago, Lynn was interviewing for the 49ers' head coaching job. Jed York ultimately hired Chip Kelly for that gig, but Kelly is now interviewing Lynn for a role on his staff.
The move, should it occur, would be a promotion for Lynn, even though he holds an assistant head coach title with the Bills. Lynn played running back for the 49ers for two seasons in 1995-96. He doesn't have any historical connections to Kelly, but must have impressed York enough to be brought back for a second look.
An assistant coach since 2000, Lynn does not have any play-calling experience, but would likely defer to Kelly in that regard, anyway.