It's just two dudes working on it, what do you think they're going to do, sue you? Licensing intricacies are (rightly) not their main concern right now.
Two dudes are still capable of finding a lawyer, especially if any lawyers in their area have pro-bono work they're being encouraged to do. Plus, they refer to this engine on the game page as professional-grade while touting how easily it can export to closed consoles. Regardless of whether you or I care about licensing intricacies, the people who control those consoles definitely would.