It's not uncommon for two different sized fans to have the same flow rating if they use the same motor.
Fans work on a pressure differential which is feed-back regulated by the motor. Basically you apply a voltage and the fan spins up until the load on the motor balances the electrical draw and stabilizes the fan speed. If the two fans have the same motor - just a different blade / housing - then they will stabilize at the same load which will be dictated by the "work" that the fan is doing (basically cfm at a given pressure). The 10" will spin faster than the 14" but they'll push the same 1550 cfm.
Now, that's probably 0psi flow. If you put a radiator in front of them then the smaller fan is trying to push through a smaller radiator cross-section which will build up more back-pressure so it's flow will drop of faster than the 14" fan.