To be fair, it is decompiled code you are looking at. If you open the dropdown you will find the optgroup with the label that says "Decompiled".
they re-implemented all functions in .net. The code is decompiled from bytecode thats why its incomprehensible and hence the title PHP to .NET and not PHP to C#.
The practical use case also seems non-existent. How can you possibly translate all sorts of functions that .NET doesn't even have?