Why does the minibuffer get updated

[Decebal <CLDWesterhof@gmail.com>]

I like to have a wordcount displayed. I tried it with the following:
    (defun buffer-count-words()
      (interactive)
      (let ((occurences
             (how-many "\\w+" (point-min) (point-max))
             )
            )
        (string-match "[0-9]*" occurences)
        (match-string 0 occurences)
        )
      )

    (defvar buffer-count-words
      nil
      "*Number of words in the buffer."
      )

    (defun buffer-update-word-count()
      (interactive)
      (setq buffer-count-words (buffer-count-words))
      (force-mode-line-update)
      )

    (unless buffer-count-words
      (run-with-idle-timer 1 t 'buffer-update-word-count)
      )

    (unless (memq 'buffer-count-words global-mode-string)
      (add-to-list 'global-mode-string " words: " t)
      (add-to-list 'global-mode-string 'buffer-count-words t)
      )

This does display the word count, but also keeps putting in the
minibuffer '<NUMBER> occurences'.
What am I doing wrong?