I wouldn’t be surprised if he does a mix of Haxe and Unity; Haxe compiles to C# too and works very nicely with Unity. In my current project I ultimately switch

I wouldn’t be surprised if he does a mix of Haxe and Unity; Haxe compiles to C# too and works very nicely with Unity. In my current project I ultimately switched off of Unity for 3D due to its less than stellar WebGL support (and I wanted to target web), but with Haxe I simply changed my target to JS and got to reuse most of my code. The ability to switch/add targets at any point of your product’s lifecycle is incredible.