Of course, that didn't escape my attention ;)
So here goes. The IC engine is a volumetric device, but lambda control of AFR is by mass. To convert between mass flow and volumetric flow, you have to know what is the density.
In the case that a car uses MAF, it knows what the mass flow is directly from the sensor and there is nothing to discuss in this case.
If the car uses MAP for lambda control, it doesn't know what the mass flow rate is. The ECU can estimate volumetric flow based on VE, load and RPM, but the MAP helps determine density by giving an idea about the pressure of the incomin…