I get this symbol when the Apple TV is successful in making the handshake with the TV. It does not mean that the media itself is DV.
So turn on the Apple TV, get the DV logo as above which then goes away. Go into Netflix. From the developer HUD:
No Dolby Vision (video-range:SDR) :
View attachment 868558
Dolby Vision (video-range

olby Vision)
View attachment 868557
note that the display video-range in both cases is Dolby Vision.
[Tried to cut/paste just the text instead of the entire screen but as you can see the developer HUD screen capture won't allow that (blacks out the movie I was watching).