A Game Freak game. Nintendo holds 33% of the Pokémon IP from a joint venture agreement which have - I suppose - a clause saying that main games being tied to Nintendo consoles.
When Pokémon Go released and become a huge success, Nintendo's market value went up, pushing them to publish a declaration saying they only have a minority stake in the Pokémon company.
And the main Game Freak dev for Pokémon games wasn't really a fan of the Switch at first and wanted to see if it would be a success before releasing games on it. Hence Ultra Sun and Ultra Moon late 2017 on the 3DS and then a remake of Pokémon Yellow late 2018 before jumping on the Switch wagon
Three companies share/own the IP, and if Nintendo has 33% , likely the other two (Creatures Inc and GameFreak) have the same percentage.
Regardless, to call it a Game Freak IP and still say its not a Nintendo IP sounds weird since the official box art states Nintendo owns the trademark and the game is a Nintendo/GameFreak/Creatures inc title.
So technically, you are right but I'm right as well in calling it a Nintendo title. If someone says its a Creatures Inc title, they would be right too.