i looked into it after the earlier post by @Panzer Zodiark because i had the same thought, but it's actually referring to a planned waterside park that was also going to be in California (it's really easy to forget that Disney has tons of resorts all over the world--iirc they essentially own an entire island in the Bahamas for their cruise line). that's probably why the existing DisneySea has the additional qualifier as "Tokyo DisneySea"
(fun fact: Walt himself was originally going to build Japan's own Disneyland in Nara after it was suggested by a Japanese business magnate but they had a falling out so the park was instead completed as "Nara Dreamland")
there's a good video about this by Defunctland, presented in the style of a Civil War documentary
Yes, the island in the Bahamas is called Castaway Cay and it is great, I've been there. Of note, DCL is not the only cruise line to have it's own island (Royal Caribbean's is Coco Cay), most of the major cruise lines have them now although Disney was the first.
On the subject of other Disney resorts, Disney Vacation Club has resorts in Hawaii, Vero Beach (Florida Atlantic Coast), and Hilton Head. They were also going to build one at National Harbor in DC that was going to be an indoor water park to compete with Great Wolf Lodge but they pulled out of that.