I feel bad for this dude. There are a lot of bitter people that are mad at him for doing what he thought was right just because they don't agree with the moral and legal situation.
Selfish for following the law and respecting the wishes of the authors of a work? Jesus, people are really performing some mental gymnastics to justify the hypothetical theft of property in this case in order to arrive at the conclusion that the finder is somehow being selfish.
Sometimes, not most of the time but sometimes, the wishes of an author are bad for the public. In a hypothetical scenario where an author wants to destroy all traces of their work, it's a bad thing to help them.
And this is about the data, and possible copyright violations, not the theft of property. Him returning the physical disk is perfectly fine. So throw out that argument.
Brahms destroyed a whole bunch of his works out of his own insecurity that they were not good enough. Brahms is now long dead but his (that were not destroyed) works live on.
If something is truly culturally significant then it should be preserved regardless of the wish(es) of its author(s) and these two hyperlinks rather easily make the case that preservation requires distribution.
How do you know it is the wishes of the authors? Blizzard didn't write the software, individual programmers (labourers) did, working as a team. Though I'd be interested to know if there's any statement from the developers of Starcraft if they did or didn't want the code shared.