And that's why he paid 20000 euros for it, right?

I don't understand what this guy is complaining about to be honest.

Is he complaining?

I don't think so? He does say he has had hurt feelings. Do you mean you don't understand why he has hurt feelings?

It's very clear that he thinks he deserves more money because the game he write short story for was a success.

20k is a very reasonable sum for this kind of gig.

For me he sounds greedy and yes it sounds like he complains (a lot)

I can't recall the details but wasn't it $20k under a $15M total valuation? Proportionally that would be $3.3M of a $2.5B valuation.

He wasn't offering a portion of the game's profits or a portion of the company. He was offering money for a work-for-hire.

At a $15M valuation, the work was worth $20k to them. At a $2.5B valuation, the work was $20k to them.