Presumably, by providing a bonus, ED wants to support open source releases. On that basis, I don't see that it matters whether it's open source because of a choice of license, or a choice of what to port. Granted, from the point of view of wanting more open source projects out there, an original open source project aces a post of an existing project to a slightly new architecture, but I'd guess ED's point of view is that it's making the Pandora more attractive as a home of open source games and apps.
Regarding source release, traditionally released software is not just privately emailed, unless it's emailed with a note that it may not be redistributed. Since the use of that phrase is part of the rules explaining why ED wants open source releases, that would imply that freely redistributable, under condition of whatever open source license the author chooses.