Yeah I can only see this working with dual AFR sensors. One before turbo and one after.
Im almost positive they are running a second set of fuel injectors right before the turbo essentially turning it into a turbine.
Tuning of the AFR and controlling the temp of the turbine is what is really puzzling me.
Burning unspent fuel in the turbo would cause some extreme temps and I imagine it would be glowing red in a matter of seconds.