@bwfc0907
This no longer happens to me. Solved it disabling CEC/Simplink in my TV settings. But I quote myself from a reddit post below
(detailed explanation). If its still not working correctly for you, try rebooting both the homepods or the ATV.
LG OLED C8 user here. Everything working fine here. I don´t use CEC because I dont like my TV to be turned off when I put the Apple TV to sleep. What if I want to play a videogame on my game console afterwards?. Or watch a live TV program?.
I also have my ATV "desactivated" as a hub (it still appears on the home app), since I was told by apple support that is better for homekit performance not to have many things active as a hub at the same time. In my case, the Homepods are the hubs of my network.
Now, taking all of this into account, this is what happens in my case.
When the Homepods are selected as the default output speaker of the ATV and I put it to sleep, if I ask the homepods (via siri) to play some music, they DO without turning the Apple TV or the TV on. Good!
If I go to the Airplay menu of an IOS device, the linked homepods are no longer there, only my Apple TV (with a little homepod icon by its side), but I can send airplay music directly from that device (downloaded songs) or from the cloud AND both the TV and the Apple TV remain off while the homepods play.
I can even turn off the IOS device and the music keep playing on the Homepods. Great!
However, If I send an airplay video from an app on said IOS device, it turns the Apple TV on.
So it seems to detect automatically if you are airplaying music from apple music to the homepods linked to an Apple TV, in which case the speakers play it directly from apple servers, or if you are airplaying a video, in which case it turns the ATV on.
Fantastic! Awesome!
In all cases, however, the home app says that the apple tv is in use... even when the homepods are playing music and the ATV itself remain off. Very curious.