Contrary to most people here, I don't think the author of Octotree has much to worry about. While there is a long list of contributors to the project, only 10 have contributed 10 lines of code or more. My understanding is that a change consisting of less than 10 lines of code can be seen as trivial and hence does not need a copyright assignment (at least that's how the FSF handles it, and they're pretty strict with this stuff).

Of these ten people, six were hired to work on Octotree, so he should have copyright for those. The other four together wrote less than 100 lines of code. If he has removed or rewritten these lines, he should be fine. (Even if he hasn't, I would consider this a very minor violation.)