So, someone played audio files on that computer, which implies heavily that the way they're producing the radio audio is to output all the audio from that computer.

That seems very foolish to me.

I was involved in more than 60 theatrical productions, most of which I was the sound designer and engineer. Almost all community threatre, but still, actual theatre.

I ran my stuff on a computer way before anyone else at that theatre did. And I quickly realized that installing mulitple sound cards was the way to go. Default sound card got muted so any audio produced didn't go anywhere. The program I used to send audio cues out talked to another card that wasn't default, so only audio I intended to go out went out.

(I had just gotten a third card so I could send a different stream to just the green room and give them a preshow countdown with music, but we ended up moving, and afterward, I didn't get involved with theatre here due to my declining health)

So this is a particularly dumb setup, in my not-very-humble opinion.