So I think he's implying that Metroid Prime 4 is made by an external developer here, but since it's not 100% clear, I went with the less strongly worded title.
http://www.eurogamer.net/articles/2017-08-23-returning-to-metroid
Metroid: Samus Returns:
Metroid Prime 4 Implications:
http://www.eurogamer.net/articles/2017-08-23-returning-to-metroid
Metroid: Samus Returns:
How did MercurySteam and Nintendo come to work together? How did that partnership begin?
Yoshio Sakamoto: For some time, I've wanted to take on the challenge of remaking Metroid 2. When considering the development I had to think about which team or partnership would be suitable. Around that time I heard MercurySteam wanted to take on the challenge of making a Metroid game. That's why I decided to meet them and also because, seeing their past work, I knew they had the talent and the knowhow to make a 2D scrolling game.
So I went to Spain and, discussing the project, I felt they really understood the series and that we could build a strong partnership to take on the project together. And, seeing their prototype, they managed to surpass my expectations which were already very high. Even in the very minute details they could get things right without me mentioning anything. I felt safe delegating to them and partnering up for this challenge.
What in particular about the prototype was it that surprised you?
Yoshio Sakamoto: The first thing that surprised me is how well the controls worked. They were smooth, swift - it matched very well to the Metroid gameplay - even surpassing the controls we've had in the past. While this game is based on the level design of Metroid 2, there were many changes made. I was really impressed. I asked the game director, who designs the levels, if he had told them to do this or that. And he said no, it was MercurySteam.
So yes, two factors - a smooth game control which fitted Metroid, and the ability to propose level design which fitted and yet was fresh at the same time. It's something which is really difficult when you think of it, and yet they did it in such a short time.
Metroid Prime 4 Implications:
This is the first Metroid from a truly independent external developer. Will we see this continue?
Yoshio Sakamoto: I don't really think of things as internal or external. What's important for me is we have a good chemistry with whoever develops the game, that they have a good understanding of the series and have the ability to add things which constitute improvements. Of course, when you deal with a partner you're not familiar with, you're not sure at the beginning if things will go well. However, if they go well, they go well. I feel our partnership was meant to be. When you have a team which is external but also from overseas, they have an even more refreshing perspective and the kind of challenges I want to keep my mind open to as well.
For Metroid Prime as well?
Yoshio Sakamoto: For Metroid Prime, I'm not in charge of that series - another producer is handling it. But generally speaking I think they look at their teams from the same basic perspective.