Every car has some leeway built into the tune. That's why the overboost limits on the 2.0's (in the ECU) are 17 something PSI even though stock boost is 14ish. In closed loop, the ECU is looking at the front AF sensor and the MAF to know how much fuel to inject. In open loop, it's just looking at the MAF and squirting fuel based on measured airflow and requested AF ratio in the ECU load/RPM table.
I think about how all that works and assume the ECU can compensate for more airflow automatically. You're correct though that the OL/CL delay will delay when it transitions to OL though. Maybe I'm comfortable because I've zeroed out the OL/CL table in my 05 ECU.
Well, he's not popped it yet and I assume this isn't a new change so, I think in practice it seems to have worked out for him.