I assume it’s a tongue-in-cheek reference to how the War Thunder forums have recently been used for multiple leaks of US military classified information.
Is an open source game engine likely to cause those War Thunder forum participants with military clearances to become more angry in debates (because they can now see how the inaccuracies in specifications would impact the performance in game) or less angry?
Either way, I doubt the impact is zero. So as something that has military effect, it might be covered under ITAR after all!