MacBook tunes TV station while updating the OS. How?

[bi11jon 0]

Story time.  I have an M1 MacBook Air that I dock to a 27" Apple Thunderbolt display.  A USB tuner is plugged into the display to get over the air TV using EyeTV 4.  Did the macOS 11.3.1 update this morning because…security.  Mac is on the update screen with the apple logo and the white progress bar.  And I start hearing what sounds like a radio station coming from my desk.  Maybe my wife accidentally played something to the HomePods? I tap the HomePod and it starts playing music. So that’s not it.  Listen closer and something is definitely playing through the speakers on the Thunderbolt Display WHILE THE SOFTWARE IS UPDATING. Then I unplug the MacBook from the display, the sound stops.  Open the lid of the laptop and the update continues.  The only thing I can figure out is that somehow a TV station tuned in and started playing audio while macOS was updating.  How did it do that?