Without sources/proof that's a statement that's not worth anything. Because on the other hand, I heard from a different race game developer that several professional drivers have said Project CARS is more realistic than the professional simulators they use in their teams. But that statement is also just here-say, doesn't mean squat without proof.
Fact is that simulations like AC and PC are now at a level where the average Joe (and yes that includes basically all simracers) can no longer discern wether a simulation is more true to life than the other. The only statements I keep hearing from the sim racing crowd are like this: AC is not like iRacing at all, so it's not realistic. Or PC is not realistic because it's not like AC. Sim racers need to get off their high horse, because you can't judge wether a sim is realistic compared to another sim, only when compared to real life.
Another fact is that both AC and PC are being used by professional race drivers and teams to train, so that should tell the general public something. The same does not apply to other sims, so that should again tell you something.
Another fact is that both AC and PC have their strong points as well as their weak points. PC has a vastly superior tire model + dynamic track grip (which PC2 will take even further!), while AC has superior suspension modeling, but is lacking in several other areas. So blanket statements like 'A is more realistic than B' are stupid. What it boils down to for most of us is mostly personal preference. I for one enjoy them both quite happily, but for different reasons.