Apple TV does support Dolby Vision. I also have an LG TV and the Dolby Vision logo appears when you change the mode from HDR (and vice versa) If you have already played a DV file the next one does not make the DV logo appear again.
It’s likely this particular video is a flavor of Dolby Vision which Apple doesn’t support. As @Totalsmokes mentioned, some apps will force DV output when they should be playing HDR, but Infuse will not.
If you can download the MediaInfo app and post the detailed specs it would help us see what type of Dolby Vision is inside this file.
Dolby Vision has many different flavors, and it’s hard to keep track of them all. Infuse will fully support as many types as possible on Apple devices, and fallback to HDR for those which are not supported. This results in the highest possible level of color accuracy for all videos.
In other apps, you may be seeing your TV switch to Dolby Vision mode when the actual video is playing in HDR. This is commonly referred to as ‘fake’ Dolby Vision, and will result in inaccurate colors. The thread linked above has a lot of info on the topic if you are interested.