Don't believe everything you read: based on my observations of the Disney show in question, it's most definitely HDR. I'm not sure what went wrong with that person's analysis but the show was graded with Dolby Vision and looks great on an OLED display; HDR isn't always about blinding "look at me" light sources!
Meanwhile, this week's episodes look to be playing in HDR10 again - except, not surprisingly, "Morning Wars", which continues to play in Dolby Vision in Australia.
One thing I've observed which may or may not be related; I notice Apple has started adding credit screens for foreign-language dubs at the end of a show's credits. But "Morning Wars" has no such screen (not surprising, I guess, since the only country that gets it is an English-speaking one).
Could it be that adding those credits at the end (probably as a separate, linked stream) be causing the HDR flag to be sent incorrectly? The actual video streams still have Dolby Vision listed as their stream type, and still seem to play correctly in Dolby Vision if you force it on as the default video output.
But that's all we can do in the absence of any word from Apple - guess and speculate. Hopefully this press coverage might start to get the word through to the TV+ people, who don't seem to have noticed the problem after four weeks of it happening...