Surprising HomePod/iTunes connectivity

I’ve noticed something interesting about iTunes and the HomePod that I haven’t seen reported anywhere. If I’m playing music from iTunes on my Mac, and I’m using both speakers next to my iMac (via direct connect wiring) and my Home Pod, which is in my kitchen, about 20 feet away (via AirPlay), then commands spoken to Siri on the HomePod in the kitchen will control iTunes on my Mac. If I tell Siri on the HomePod to pause or stop, then it will stop music playing on my Mac; if I tell Siri on the HomePod to lower the volume, then it lowers the volume within iTunes on my Mac, not just the volume of the HomePod!