He is, undoubtedly, one of the people who worked on a part of the game, yes. That counts as "helping create the game". And claiming to have "helped create the game" is not the same as claiming to be "the creator" of the game.
It absolutely reads as if his contribution is significant enough that he should be be considered one of the creators.
> giving money to back-office staff who had just arrived in the last year, and had zero creative input into the game [...] I had helped him create the actual game
The way he puts down regular employees, making it sound like his poem is obviously more important than whatever a mere employee does.
Yes, he considers himself "one of the creators of Minecraft". Because he is one of the creators of Minecraft; he created a part of the game. He doesn't consider himself "the creator of Minecraft", as you claimed.
You can think he puts down regular employees and makes himself seem more important than is warranted. You may think his contribution is tiny compared to the contribution of people who marketed the game or made the website. I may even agree. But that's not what I take issue with. I take issue with you misrepresenting his words by claiming he thinks he's "the creator of Minecraft", which is completely unfair.
It's more complicated because he's one of the latecomers : by the point he was asked to do this work Minecraft had already been released and was already a massive success.