Improper shielding is an assumption with no evidence as yet. I also mentioned that the ease of verifying the explanation should be a factor. Changing software is usually very easy.
It's so common that it's not an unlikely starting point. EMC is a major issue in high frequency electronics design and the raspberry pi had a history of having to redesign certain parts because of not having enough shielding.
Absolutely, and this was before the Pi had built-in Wifi. The norms you have to comply for are immediately a lot stricter as your device falls into a different category (telecommunications devices).
wrapping tinfoil around an hdmi plug/cable isn't particularly hard either :) chips are harder but at least you rule out the cable. HDMI cables are ridiculously finicky if you've ever tried to get anything more than the lowest common denominator 1080p going on them.
I don't agree that wrapping foil is a great way to 100% rule that out as there is room for error. Using different cables/dongles would be better and they already tried that.