Society grants you the right to enforce what we call intellectual property. Enforcing that concept is rather new, and some of humanities biggest cultural works predate it.

The timespan for which we grant a creator the sole right to decide about his work is arbitrary and, last but not least, almost all of our cultural works are derivative in nature, so what actually is our own work is equally arbitrary defined.

In the existing framework he can do what he did, but the current one is not the only possible.