Hello halw2k,
Thanks for taking the time to reach out here in Apple Support Communities. From what I understand you purchased a movie using the VUDU app on your Apple TV, but your Apple TV library does not show the correct format of the movie purchased. Is that correct?
If so, have you tried restarting the Apple TV to check the recently purchased movie?
That may be a helpful step to try since all the other movies purchased in VUDU seem to show the correct format.
Restart Apple TV
Should the issue continue you can also try reinstalling the VUDU app as well.
This can help you isolate the issue to the VUDU app itself.
Move and hide apps on your Apple TV
Does the actual movie play in HD instead of HDR? Should that be the case, I would recommend reaching out to VUDU support directly. Although the movies are shown in your Apple TV library, the content is still being streamed from the VUDU app itself in this case.
Keep me updated on your findings!
Regards.