The only way to prove it would be to put the old one back on the car and see if it goes slower again. I think as said before that it may have been a lazy sensor at some point, which then fixed it's self in removal and refit.
Also i know that the intake system is sensitive to airflow speed, if your in take sensor has a too big pipe, it can't measure the in coming air accurately. Could be the same for the exhaust...
Or a dirty sensor, that got cleaned up on removal ?