From close,

If the file handle came from a piped open, "close" will additionally return false if one of the other system calls involved fails, or if the program exits with non-zero status. (If the only problem was that the program exited non-zero, $! will be set to 0.) Closing a pipe also waits for the process executing on the pipe to complete, in case you want to look at the output of the pipe afterwards, and implicitly puts the exit status value of that command into $?.

In this case, I'd say that closing prematurely the filehandle raises a SIGPIPE in the subprocess (as explained in the documentation). If this causes a non-zero status, you get a close error although no system call failed.