He's talking about the actual rate of fire vs. the sounds AH is capable of. The noticable, or slower guns, are just that - the 109/190's 30mm Mk108, P39's M4, Yak9T's NS37, and Hurri IID's 40mm vickers. The sounds replay after they finish playing, so if you hold down the trigger in a slower firing rig, the sound may not sync up with the actual rate of fire. He's saying if the Wirbel actually sounded as it would have in real life, you may experience a massive hardon after firing... but actual effects in game would be the same as you already experience
BTW - was that an actual recording of a 110 unloading moot? Obviously not in the air... more like testing convergence during maintenance?