This is almost correct. If this was decided in the US, his discussions and acceptance of payment gave Mojang a non-transferable license. During the sale to Microsoft, he was a stakeholder. Microsoft failed to acquire a license, which was why they were trying to force him to sign a contract with terms - of perpetual transfer - that he did not agree to. Mojang needed that signed otherwise Microsoft needed to negotiate a license or purchase from him directly. Microsoft did not do this so they don't own it nor did they have the right to distribute his work until he public-domained it. They are still guilty of infringements up to the date he public domained it, but he seems to have released he right to pursue this as part of this essay.