I would assume that he gets AFR by calculating it from Speed Density mode but I assume that that is off. The AFC see (
ZZ Performance ) scales the MAF frequency telling it that there is less or more air depending on how the PCM calculates load and timing both might be off due to this since the car would be running in SD mode and using the MAF I assume that that was the normal config for the engine to run.
If you are not modifying the PCM but tricking sensors then you are not tuning. If you are running lean you should have a WB02 or at the least a EGT sensor to monitor the temps. If you get to hot it can burn up the exhaust valves and possibly throw a chunk in to the cat of let it dance around in the cylinder.
I do some PCM tuning and am looking to later work on running a hybrid open/closed loop system for lean burn when trying to keep emissions close to stock IIRC that would be running 15.5:1 to 15.7:1 I might be wrong on the AFR but do not have time to look it up as I'm late for class.