I’m inclined to interpret it as a mistake.
My understanding of the availability of this feature comports with @spamoni’s post. By that I mean that I’ve been able to get OG and Pan v3 cameras to function as accessory chimes by selecting the appropriate options in the settings for the Video Doorbell v2—not by using Rules (though I’m aware of the “Ring” Rule Action, as well).
It my particular case, once I enabled that feature, I’ve so far been unable to disable it. That’s a minor annoyance that I can live with for now, hoping that it’ll be ironed out in future app/firmware updates.