The ability to translate between two programming languages is called a compiler. There is theoretically nothing stopping anyone from writing a anything-to-anything "converter" (you mean compiler).
The program the poster was referring to is actually a disassembler, taking Microsoft IL (assembly for the virtual machine) and converting it to a .Net language. So you might;
- compile C# to Microsoft IL - decompile the IL back to IronPython - use that as the basis of a CPython version.