Well first things first... if I'm reading it correctly (my german is a bit rusty) I think they have the airflow a bit confused. They claim that the fan is able to put out 33 cubic metres/minute. That's around 300 CFM if I'm not mistaken.
If what they really mean is 33 CFM, then they are not using the pabst 12db fan, because that only put out about 19 CFM.
Now the 26 db Pabst fan puts out about 33-34 CFM so that is another possibility.
However, they write that the fan runst at 1500 RPM's which would make it the 12 db pabst. Am I rambling here?
In any case... I think the 12 db claim is based solely on the pabst specs and nothing else. And, there seems to be some confusion about the fan specs to say the least!