rbhfan,
There is no way for Netflix to know if it is streaming to a projector, or streaming to a TV. That is ridiculous. There is something else going on there.

You said you upgraded the customer's service to 4K, are you sure? Because currently Netflix has 3 levels:
$7.99 per month - 1 screen and SD.
$9.99 per month - 2 screens and HD video.
$11.99 per month - 4 screens and 4K video.

The only other thing that could cause 4K to fail to work like you are describing, is if the proper EDID is not getting done between devices. Check your setting again and use a test TV also.

Oh also, obviously not everything is available in 4K on Netflix either. Make sure you are selecting a title that is available in 4K.