I think you're the one missing something. I just searched that exact phrase and all the sources I can find says they play the sound through the interior sound system. Can you find me a source that says otherwise? I can't.
https://www.maxhaust.com/en/accessories/v4-ab-022023/active-... https://schawe-shop.de/en/bmw/bmw-5-series/bmw-5-series-seda... (no product page) https://ixsound.eu/ https://milltekshop.com/active-sound-control-single-sound-ge... https://thor-tuning.com/eu/shop/thor-electronic-exhaust-2-lo...
From the descriptions it's unambiguous that these add-ons are not pumping 100dB into the car's interior.