Why is it laughable? I'm not disagreeing with you: I am rather curious.
The idea that "I'm throwing the output of some randomness source at Diehard, and if Diehard says it's good then the source provides information theoretically secure random numbers" is a category error at best.
I see it as this: if the randomness source cannot be one more time put into the same conditions that it would start repeating the same sequence, and its output is random enough (i.e. passes the tests), it may be considered safe for OTP key data production.