Compression ratios. Most factory 2.3 turbo motors will have dished pistons and about an 8.0:1 compression ratio. Naturally aspirated (non forced induction) motors are going to have a flat top piston and a higher compression ratio, about 9.2:1 according to him. He's saying that if it has turbo pistons and the lower compression ratio, it might not have as much power and run as well as the higher compression ratio.
Generally speaking a higher compression is going to generate more power, but to much compression leads to detonation which is bad. Turbo motors usually start with a lower ratio, because when that additional air gets forced in its going to increase a lot.