They probably manually inlined a line like

    int num2 = _linqitems[i];

from the decompiled output. I'm fairly certain that if the transformation wouldn't result in compiling code, the compiler would refuse to compile it, resulting in no assembly to decompile. They also noted somewhere to have run the System.Linq tests and only one edge case involving Min/Max and NaN failed. Tests likely wouldn't run either if the code didn't compile.