That is correct. Different interfaces have different requirements.
The same resolution applies to DisplayPort++ as it's really HDMI signals over a DisplayPort plug (in layman's terms).
These parts don't do 5K either, the DisplayLink DL-6950 does.
The Wikipedia page is not the specification used to test or certify any product. The Wikipedia page does not state it is a mandatory requirement, does it? You have missed replying to that question.
If you find contradicting information in the HDMI
specification, I will be delighted to go to engineering and ask the question. But I don't see myself using Wikipedia as the source to report a bug... You could clarify the Wikipedia page as it's free to edit or ask for clarification before doing so.
The fact that the chip doesn't do 4K over HDMI can be totally irrelevant to an end product. One illustration could be the
Plugable UGA-4KHDMI graphics adapter.
Should you have questions for your design, we can work out the details for what is the most suited to your project.