It’s not. You keep insisting that ^D doesn’t send EOF and yet:

$ stty -a | grep eof
intr = ^C; quit = ^\; erase = ^?; kill = ^U; eof = ^D; eol = <undef>;
$ man stty |grep -A1 eof |head -n2
       eof CHAR
              CHAR will send an end of file (terminate the input)

^D is the EOF character. The thing is that in C every line of a text file must be terminated by a new-line. And so, when you end a file with ^D without a return, you get funky results.