It's an OOP language ( looks like C#) that compiles down to OOP C.
BTW, early C++ compilers also used to compile to C, but that feature was «removed» long ago. Nearly none of the well-known compilers have ever implemented it. I think that C++ was mostly compiled this way from 1979 until approx 1987, long before I ever heard of it, and before nearly anyone had heard of it.
That's too bad because it's a great feature to have.
The GObject method is pretty clever. It allows you to abstract objects in an XML format. Then, based on those abstractions, you can introspect them for their behaviour and link them into almost any language.
I wonder how difficult it would be to do something like that with PD's object system?