The IP rights of Wonder Boy are super confusing, let me clarify a bit:
This game IS a licensed sequel to the old games, and they've paid for the rights. Due to Sega's arrangement with Westone, the rights to the names "Wonder Boy" and "Monster World" are owned by Sega, but everything else, including characters, lore, music, etc was owned by Westone (and later transferred to LAT after Westone folded), and that's what they've licensed here.
The weird character swapped versions that Hudson did were actually not because their arrangement didn't afford them the rights (as most people assume), but because Hudson wanted to be able to own their own IP. In changing the characters, they could then make their own "sequels" without having to pay Westone (as they did with Adventure Island). They COULD have used the Westone characters, they just chose to swap them for ones they could OWN.