Correct.
Can you then tell me “how special” a Theme has to be, to be accepted for the Marketplace?
If you follow the design and code guidelines on the submission page linked above and it’s a sufficiently unique design (i.e. not a variation of an existing theme in the marketplace) then there’s a high chance it will be accepted.
For example, would be one of the Themes from Anders Noren from this Topic been acceptable?
If they are well coded then sure, they would be acceptable. One thing to be aware of if you’re copying other’s work is to respect copyright and licensing - the design of those themes is still copyright of Anders Norén and the code is licensed as GPL v2. If you get permission to re-use his designs you’ll likely still need to release them under the same GPL v2 license.