My evidence is that the entire page is basically just to shows CIL's output on various pieces of code, and CIL's output is linked on the page and looks like this:
/* Generated by CIL v. 1.3.7 */
/* print_CIL_Input is true */
#line 1 "cilcode.tmp/ex30.c"
int main(void)
{ int x ;
{
#line 2
return (x == (x != 0));
}
}
From that I think it's safe to say that it's talking about 'x' being an uninitialized variable in a function (Because that's what they put into CIL). This code definitely has the issue from UB that I described above.