This is a pretty straightforward case of copyright and perhaps trademark infringement; I would be pissed off if I were Wolfire, too, but the reality is, they just need to send a DMCA takedown notice if someone's infringing on the Lugaru trademark or copyright on the levels / game data.

If they had never marked it, or placed the mark out in public domain, or bulk licensed the content out with their content release, then this would have absolutely been in bounds to do, although annoying and shitty by the knockoff developers.

Anyway, Kotaku doesn't really dig in to the legalities here. The wolfire release blog post clearly states that the game content is not for commercial release, so I'd think this is the way for Wolfire to approach it.