Maybe it has an aftermarket Detroit Tru-Track Limited Slip Differential, and he's calling it a locker, unless the original diff. blew out and he replaced with an axle with the locker and wired it up somehow. If that's the case and it's a 4x4, I think he would have had to have the big tow pkg. for the new rear gears to match the front.
You're correct ... about the off-road pkg. and switch.
You're correct ... about the off-road pkg. and switch.