I think I solved the mystery of why the HomePod suddenly interrupts us during conversation at our house... It turns out the HomePod not only responds to "Hey Siri" but also my wife's name, "Izumi" which coincidentally has a pair of vowels that rhymes with "Siri", but otherwise does not sound anything like it. It may or may not require the "Hey" in front of it, depending on whether the name is used at the beginning or within a sentence. Normally this would be an issue, but requests like: "Hey Izumi, is it raining outside?" or "Hey Izumi, turn off the TV" gets answered/performed by the HomePod. Other requests like: "Hey Izumi, can you get me something to drink?", or "Hey Izumi, make me a sandwich!" gets the "I'm sorry, I can't do that on HomePod" or a similar response. So to her, while it would normally be annoying, it winds up being a convenience.