Kinda difficult to see, but it could be anything from what I can tell, really. Java uses var yes, but so does C#. Can't really make out the rest of the code to determine what it could be, and there's a chance that they've made their own libraries that would also affect its appearance a bit.
Those are my thoughts, but I was very interested to hear all of yours and look forward to seeing what they actually used! -CodeVortex
I think that modding and scripting are separated things because in the trailer they have their own sections. and because I think that would be a smart move allowing mods to be developed in a more fast language like C# and JS would being the equivalent of Minecraft command block, (easy but slow).
And for the server, they would still be able to use Hypixel codebase with some refactors probably.