In your OP you did mention that the owners of the code claim it to be open source. That should have raised flags right there but I chose to address this question from the perspective of ownership. I think that a lot of so called open source is protected under any number of copyright and patent conditions.

Firefox is open source (community built) and while you can promote the browser, you cannot sell or distribute builds. Only they can. I also don't believe you can implement their code in your projects. Open Source does not necessarily imply public domain.

OpenOffice might fall under this umbrella as well, but then in this whole open source question I confess to be talking through my hat, and cannot give accurate information in this regard.

It's good that you are researching the definition, implications and provisos of open source. Perhaps you might even consider a new thread on the topic when you have some clear answers and guidelines to share...